One of Ben Tennyson's alien forms in Ben 10: Alien Force is the awesome Alien X, capable of reshaping the very fabric of the universe at whim. But there's a catch: Alien X has three separate personalities, Serena, the voice of love and compassion; Bellicus, the voice of rage and aggression; and Ben, the voice of reason. In order to perform any action at all, up to and including speech and physical movement, two of those three personalities must agree to do so. Considering the other two personalities have been arguing for an eternity before Ben's arrival and aren't likely to be convinced by a fifteen year old, this doesn't happen very often. For example, when he arrives, they present him with the question of whether or not they should save the dinosaurs. To them, this is not an impractical question: they could reverse time and save the dinosaurs... although Ben, having evolved from creatures who thrived in the wake of the dinosaurs' extinction, would create a paradox (no, not the time traveler) if he did so.
The Omnitrix was this throughout most of the original series. The most powerful weapon ever created? check. Capable of adapting to any situation? check. Nearly indestructible? check. Unreliable, questionable battery life, target for the most dangerous criminals in the universe? ummm... check.
With a weapon designed by enslaved Vort scientists for their Irken conquerors, what do you expect?
Another thing to note is that, even if the Megadoomer's cloaking device did cloak the pilot, it would still be useless as a stealth weapon because the machine is so bulky and heavy that it leaves a trail of destruction and footprints in its wake.
Invader Zim runs on this trope. One of the biggest examples is in the episode "Battle of the Planets." The Martians worked themselves into extinction turning Mars into a giant spaceship. When Zim asks the Martian hologram why they did that, it said "Because it's cool!"
The Technodrome from the original Teenage Mutant Ninja Turtles cartoon wasn't just awesome - it was badass. It looked both cool and formidable, was capable of surviving in any environment from outer space to under the ocean, and was equipped at various points with a time machine and a fully fledged robot army. One problem, though — there was no power source capable of powering the Technodrome for any practical length of time, making the vehicle essentially worthless. The two biggest storylines over the course of the series were Shredder's attempts at killing the Turtles and trying to jump start the Technodrome.
In Turtles Forever, once the 200X Shredder applies some of his own technology, he's able to unleash the machine's true potential and nearly destroys the entire multiverse with it. Even more awesome is that it becomes the only thing powerful enough to stop the super-sized Shredder!
In The Venture Bros., a series set in a universe that runs on Awesome, but Impractical, one particular item stands out: The Monarch's Battle Panoply. It is a solid suit of complete body armor that happens to restrict 100% of his body movements and makes him spin around uncontrollably in flight, shooting lasers everywhere. To deploy it in the field, two people had to help him don the armor, and then his henchmen had to move him around like a statue. One henchman even died deploying the wings. Naturally, this didn't end too well for him. Justified somewhat in that it had never been tested.
In a complete inversion (i.e., Boring Yet Practical), as well as a case of Chekhov's Guns, we have the wings worn by the Monarch's henchmen. For nearly two seasons, they show no purpose other than being part of the costume and the butterfly motif. During the final episode of season 2, however, it turns out the wings can fly. You heard right: the wings actually double as jet packs, allowing the henchman to fight off Phantom Limb's army. However, after this, it is never brought up again. A goofier aspect of this is brought up in season 4; the wings are constantly extended, and every door in the Monarch's cocoon base tapers to a point at the top. The henchmen can barely walk around without their wings getting in the way.
Rusty himself once designed a Laser Sword but ended up scrapping it before he could get it to work because the military pointed out they don't use swords anymore. He attempted to sell it to Kenner (the company that makes Star Wars toys), but they didn't go for it either as it cost two million in parts alone.
This pops up quite a bit in the show. Brock frequently avoids using any Bond-esque spy gadgets in favor of his Bowie knife, explaining they either rarely work or are too specialized to be really useful. In an early episode, Dr. Venture invents a "Joy Can" that fulfills the every desire of whoever's inside and winds up sealing Brock and the boys inside it. In yet another episode, Venture needs to use a shrink ray his father invented (to win a bet) only to find it's fallen into disrepair and he's not a skilled enough scientist to fix it.
A lot of Megatrons from different series turns into different modes. Beast Wars had a T-Rex mode. The Unicron Trilogy Megatron had turned into a tank, a jet and a race car etc. G1 Megatron, by far the most memorable Megatron, however, turns into.....a pistol. Never mind the fact that he could shoot at his enemies when he's in robot mode anyway, or the fact that every one of his minions had guns of their own, but when he turns into the pistol he will need someone to actually wield and use him (so that means 1 less fire support) and also his gunbarrel turns significantly smaller so the damage output his makes would likely be less then if he just aimed his arm cannon!
And he always seems to give himself to Starscream. One wonders why he was never stepped on or stolen.
In The Powerpuff Girls, the Professor builds a giant robot called Dynamo after seeing the girls get hurt while fighting a monster, so as to protect them. However, the girls state that they don't really need Dynamo since they have superpowers. Truth be told, Dynamo does end up stopping a monster the girls couldn't defeat by themselves, but it also ends up destroying most of Townsville, so the Mayor orders them never to use it again.
Buttercup thinks her tongue curling ability is an awesome power because Blossom and Bubbles cannot duplicate it like they could her other powers. But everyone else—even the narrator—thinks it's lame.
The title Mecha of Titan Maximum. A good idea in theory, yes. But, there's a few hitches. It's ludicrously expensive, piloted by half a team of idiots, and usually eschews even more expensive weaponry to, in Palmer's words "Punch the fuck out of it!" It's small wonder Titan's government retired it at the first chance.
Count Duckula's Castle Duckula - It has the ability to magically transport itself and its inhabitants anywhere in the world, but it always returns to Transylvania at dawn, Eastern Transylvanian standard time. Naturally this leads to some missed flights leaving Duckula and his staff stranded. Not to mention the castle itself often misinterprets its master's commands and flies to the wrong place.
"Pegleg" Pete's RV in Goof Troop. High-tech, flashy, and BIG, it slowly fell apart the minute he started to actually drive it. Come to think of it, this was a running theme for Pete throughout the show — a super-duper home entertainment system was another one of his "follies."
Archer himself is an example. When in the field he's singlehandedly captured an entire space station, defeated a cuban hit squad armed with automatic weapons using only 2 molotov cocktails, an ice scoop, and a broom handle, and sneaked past an entire armed force of enemy agents while a liter low on blood and drunk. His behavior at literally everything else, however, makes his inhuman abilities wildly impractical, to the point that he's been deliberately shot three times by his own coworkers for how much he irritates, belittles, and berates them.
An episode of Aqua Teen Hunger Force sees Shake extolling the eHelmet, a helmet that has cell phone and text-messaging capabilities (and, as Carl shows, can display some really out-there porn), but requires a really heavy battery pack to operate it. It's little wonder Frylock sticks to his small, lightweight cell phone, which does all that and has a 14 Megapixel camera. Shake still tries to one-up Frylock with a camera attachment which comes with IV drips, as at that point it is so heavy Shake cannot move at all. Shake, being too prideful to accept his eHelmet is a flop ("The mouth is a primitive hole that will soon be phased out!"), tries to counter Frylock's MP3 player, which has space for 10,000 songs, with an "e-iano", which can play every song out there by converting it to a single ragtime tune. There's also no way to turn off the e-iano, so you must buy a silencing cover or add the eToms to drown it out. At that point, the weight of the eHelmet + attachments causes Shake to sink into the ground, so he adds a pair of robot legs. Not only do they suspend the user upside-down, Carl's eHelmet legs begin humping Shake's (probably because of all the porn), prompting him to order an Artificial Intelligence attachment. Said AI is at the level of a four-year-old, and while it does repel Carl's eHelmet's advances, it also likes to go swimming. And the eHelmets aren't waterproof.
Meatwad:The moral of this story is that technology... and that nice yellow padded chair in the living room is mine from now own. I call it.
In the My Little Pony: Friendship Is Magic episode Inspiration Manifestation, the puppet stage Rarity initially made may have been aesthetically appealing and elaborate, but it was rejected by the puppet-master due to being difficult to move around and being too cramped on the inside for him and his puppets.