Despite how badass motorcycles are, sometimes they're just not quite right for the situation. For one, they're large, they're noisy, you need to stay fully on them, it's hard to fight hand-to-hand and they can't maneuver well in tight spaces. So for some, roller skates are better.
A person using this is very often a kid or has a childish personality, and are also often a Fragile Speedster. Also very often shows that the person is a Badass. If they're in an especially big hurry they can even add rockets for a little extra boost.
This trope frequently occurs in Humongous Mecha. Logically, they are there to make it easier and faster for the mecha to move around, but also to appease lazy animators. The wheels will either be on the feet, or the feet will transform to reveal wheels. Caterpillar tracks are common substitutes for wheels. Spider tanks under 4 meters (roughly 12.5 feet) tall will normally feature wheels on the bottom of their feet.
Not to be confused with Wheel o' Feet. A form of Travel Cool.
The Knightmare Frames in Code Geass use roller wheels called landspinners as their primary method of locomotion (until flight packs get mass-produced). Played the most straight with the Shen-Hu, whose landspinners are actually designated "rollerblade-type" and are formed by a pair of blade-like projections on the feet which form down, as opposed to the wheel being on a separate limb as with all other models.
Likewise Eureka Seven, though since they spend the vast majority of their time in the air, it's rarely seen.
Although it's worth noting that they also fold into three-toed feet for climbing up sheer faced walls, or occasionally, hanging from the ceiling.
Sakura in Cardcaptor Sakura skates to school every day and uses them in battle on occasion, with one particularly impressive example when fighting The Fly.
But of course, the first skating Humongous Mecha is the MS-09 Dom from Mobile Suit Gundam, which uses jets built into its legs to skate along the ground instead of running.
This is taken to an extreme in Super Robot Wars Original Generation: Divine Wars, in which just about every mecha not capable of atmospheric flight can instead hover-skate over not only the ground, but the water as well.
Jango, the Humongous Mecha from Bakuretsu Tenshi, has rollerskates and a jet engine. Actually has a function, as they're meant for speeding through Tokyo's highways.
In the first episode of Kaleido Star, Sora Naegino catches a pair of loaner rollerblades to chase after a luggage thief, going awning-hopping to finally track him down. Her rollerblade skating abilities come handy later, when she has to train for a role in Dracula that includes ice-skating. Too bad she loses to May, a top-notch ice skater.
Roll Cake-chan from Sorieke! Anpanman. She is a rollerskating girl who loves making roll cakes.
Both Anpanman and Baikinman also did this in the intro for the Edutainment specials.
Air Gear uses this liberally with the ATs, which actually fly.
Technically, they don't let you fly, just use crazy amounts of momentum to launch you in the air really far. (Most of the cast DOES end up flying later, but it's not because of the ATs.)
To give an indication of how far these things can throw you using only momentum and center of gravity adjustment, the current record for longest no ramp(unless you count the starting pad they jump off of, but there is no ramp of the end of it) leap is 35.09 meters. For those who are not on the metric system, and are to lazy to do the conversion, that's 115ft 1.5in.
Lil Slugger of Paranoia Agent wear rollerblades, though he isn't as good as he is utterly terrifying.
The Alien Party in Alien Nine chases extra-terrestrials around their elementary school on in-line skates. Armed with butterfly nets. And symbiotic aliens as helmets.
Suzuna from Eyeshield 21 loves to wear these, even when cheerleading. Her ice-skating skills are also top-notch, too.
Genki in the anime version of Monster Rancher uses them very often in battle.
The titular machines from Rideback are normally bikes that can transform into small-sized mecha with the bike wheels instead of feet, allowing their pilots to cover both Badass BikerandRollerblade Good depending on situation.
Minamo from Real Drive has shoes that sprout rollerblades at opportune moments.
Trigun brings us Rei-Kei The Blade, a samurai who uses Dangerous Forbidden Techniques with his katana against gunslingers. To compensate for his reduced effective range, he wears rocket-powered roller blades. Somehow, Vash manages to keep a straight face while fighting him.
Konoka Konoe from Mahou Sensei Negima! skates her way to school. This is used to contrast her with her panting, diligently running companions and thus display her easygoing, carefree nature.
The Humongous Mecha from 20th Century Boysmust be bipedal according to The Book of Prophecy. The scientist kidnapped to design it emphatically points out that this is completely impractical. His solution is to treads under the hollow feet support the weight of the machine, while the feet only lift up and down.
The Triplets from Dogma, being roller-hockey themed mooks.
Subverted in Jackass: The Movie, which has them trying rocket-skates which sent the guy flat on his ass after a couple feet, showing that the rocket powered skates aren't quite Truth in Television yet.
There is a scene in the live-action Transformers film where Bonecrusher transforms into his robot form and proceeds to rollerblade down the highway after the heroes, only to be blocked by Optimus Prime when he turns around to do the same.
Sideswipe, a character in the sequel Revenge of the Fallen, literally has wheels for feet. Damn, he's good...
Prayer of the Rollerboys! In the wake of the rollerblade fad, this Corey Haim vehicle features a dystopic, near-future LA where the toughest gang on the streets is a bunch of teenage white supremacists who ride rollerblades into their rumbles.
In Monsters vs. Aliens, Ginormica uses cars as roller skates to escape from the alien robot. Later she uses the same trick with hoverboards.
And in the video game her car-skating becomes the whole shtick of her levels.
Rollerblade is about a group of roller-skating nuns who battle monsters and mad scientists with their magical healing switchblades. And hang around naked a lot.
In Robots, Cappy (voiced by Halle Berry) kicks down wheels embedded in her feet and "rollerderbies" a few bad guys to help Rodney and Bigweld escape, then later in the underground battle with Madame Gasket (voiced by Jim Broadbent) she uses them again.
Whip It is about a misfit who discovers that she has a hidden talent when she joins a roller derby league.
Subverted in World War Z where a mercenary tells how he saw a kid on roller blades wielding a hockey stick with a cleaver at the end of it. He was grabbed at the ankle (making him fall), and then dragged into a gutter. And then called a "dumbass". By Paris Hilton.
In Tomica Hero Rescue Force, the late-series Humongous Mecha Rescue Max is made from the parts of two large rescue vehicles, and thus even with "legs", it's inevitable that it's going to have to skate around on wheels. The rockets only come out when it's time for the Finishing Move.
Father Dougal Mcguire from Father Ted had to give up rollerblading as a vice for Lent in one episode.
One episode of Mythbusters had Jamie, in the course of building a hovercraft, zooming across the shop in skates wearing a homemade jetpack made from several leaf-blowers grafted together.
Rollergames was a 1989 television series that tried to turn the sports of roller derby into a theatrical show. It only lasted one season, but it had several tie-in products, including a Pinball table from Williams Electronics and an arcade game and an NES game, both developed by Konami.
The mecha of Heavy Gear run with retractable roller skates for high speed movement over flatter ground. No rockets, and usually doesn't say much about the pilot's personality — they're just around to make transportation easier. Carried over to the video games.
Heavier models instead have caterpillar built into their feet in place of wheel, but they work just the same.
Mage: The Ascension had rocket-powered rollerblades that could run up walls. And along ceilings. And reach 200 MPH in 20 feet. Failing the rather difficult athletics rolls with them spelled painful disaster.
One of the cyberbits you could've put on in Shadowrun (at least its third edition) was, basically, in-line Gadget skates.
In the d20 Modern sourcebook Cyberscape, you could get retractable roller blades as a cybernetic implant, allowing you to improve your move speed quite a bit.
Fatman from Metal Gear Solid 2 is an overweight demolitions expert. Including his blast suit, he weights half a ton...so, obviously, he needs to wear roller blades for increased maneuverability. Predictably, he falls down a lot, and has trouble getting up.
Clara from Power Instinct has the ability to turn into an age-progressed version of herself decked out in an odd, Stripperiffic costume and rollerblades. One of the games makes this special form of hers a dedicated, selectable character.
Yang from Street Fighter III, is often seen wearing a pair, usually in cut-scenes, but never in actual combat.
Area, a Mad Scientist girl introduced in Street Fighter EX 2 Plus, wears a pair in battle along with a big gauntlet (actually an invention of her father).
Front Mission 4 has this in its intro video in a most certainly badass way.
This is also something that can be upgraded onto humanoid leg parts, allowing equipped wanzers to move in straight lines (such as down streets) much farther than they could walk. They can't actually turn while using these though, unlike in the cutscenes.
Mega Man himself gets some in Mega Man Legends. Except that they do away with wheels entirely and use jets.
Averted in Tony Hawk's Pro Skater, where bladers are whiny brats who are to be thoroughly embarrassed by the skateboarders.
Ratsel Feinschmecker's Aussenseiter of Super Robot Wars is a Super Robot with large wheels attached to it's feet that allow it to skate along the ground to make fast attacks.
Steel Battalion: Line of Contact changed 5th gear into a wheel mode. Fast and smooth on level terrain, but worse for climbing and much harder on the balancer during turns, increasing the likelihood of the VT tipping over if the pilot isn't careful.
Pokémon X and Y feature rollerblades as a form of transportation for the player and has Gym Leader, Korrina, being a big user of them. They're much faster than the Running Shoes (which you now start the game with) and since they're controlled with the Circle Pad, they also let you break free of the Invisible Grid for the first time in a main-series Pokémon game.
Skylanders Swap Force has Roller Brawl, a spitfire of a girl and vampire roller derby champion, who joins the Skylanders when she draws the unwanted attention of the series' Big Bad. For extra awesomeness, her roller skates don't have wheels, they have circular saws.
Clothesline, from the MSF High Forum, always, always, always wears roller stakes. Why? Because she isn't allowed to use her motorcycle indoors anymore. When outside, she uses her motorcycle. Tragically, her steering sucks. She cannot park without hitting someone.
In Transformers Animated, Bumblebee and Optimus Prime both have one of their wheels on each of their robot-mode that they have been occasionally been shown to move around on. On the other hand, Prowl has his vehicles mode wheels in his knees and can use them to ride up walls.
Optimus and Prowl only ever pulled tthis trick once though. Bumblebee used his skates alot more, given he the Fragile Speedster.
Beast Machines gives the "wheels as feet" to Rattrap. It's pretty much a hindrance to him, though.
One of the toys that Boris bought out with his enormous supply of counterfeit box tops in the Box Top Badman arc of Rocky and Bullwinkle was atomic roller skates.
Rhodey makes fun of Tony for the idea of putting roller blades on the Iron Man suit in Iron Man: Armored Adventures. Later in the season, he does just that.
Starlee Hambrath, from the "Fast Forward" season of Teenage Mutant Ninja Turtles (2003) is never without her two-wheeled inline skates, which appear to be built into her jumpsuit.
Loogie from Get Ed has a pair of jet-propelled skates. While he may or may not qualify completely for Fragile Speedster status, he's certainly the most...eccentric...team member, talking to his sock puppet catfish Dr. Pinch.