In reality, frags actually produce rather small explosions, without the enormous shockwave or fireball that normally accompanies a grenade explosion in an action movie. Structural damage to the surrounding area is not significant unless flammables are present, and people don't get blasted into the air. The reason for this is that a frag grenade is designed to transfer as much of its chemical potential energy as possible into the kinetic energy of its shrapnel, rather than producing a powerful localized shockwave and fireball. Therefore, a frag grenade explosion in a typical room will leave it looking much the way it was before. However, a close inspection of the room would reveal countless jagged metal fragments embedded in the walls, and any men in the room would be dead. Moreover, even men in adjacent rooms might be dead or injured, depending on their proximity and the construction materials used. The velocity of the fragments is such that they will easily penetrate deeply into all normal building materials, so drywall and even wooden doors would not provide enough protection. Also, the "up and over" frag explosions are also a myth: any cover is better than no cover, and smallest profile prone is better than broadside prone, but you're still guaranteed multiple wounds unless you have an incipient Medal of Honor (posthumous) candidate intent on smothering the blast, or (even less likely to be entirely successful) someone up to the challenge of speedballing a return pitch. Obviously, these aren't used haphazardly in Real Life.
Concussion grenades, to the contrary, rely on the massive overpressure caused by the explosion, which gives them entirely different application, especially due to the relatively small casualty radius (about 2 meters as opposed to 15 meters for frags). Concussion grenades are especially effective indoors, where the overpressure effect is amplified; the detonation will likely kill everybody in the room, blowing out walls and causing structural damage. They can also be used for more offensive purposes too, as their short range allows them to be effectively used to assault enemy trenches without having to worry about shrapnel cutting down your rushing allies. Contrary to Hollywood portrayal, these are very dangerous: the overpressure is extremely high in the casualty radius, breaking bones and disrupting vital organs. The blast wind is capable of blowing people into the air, which is extremely problematic if there happens to be a stationary object behind them. Those on the outside of the explosion will suffer fringe concussive effects, getting extremely disoriented and becoming easy targets. That said, they're still very uncommon in modern militaries, as rushing enemy defenses across open ground went out of style about a century ago, and there are more efficient ways of blowing apart buildings than lugging around otherwise ineffective grenades.
The record for a piece of shrapnel sent out by a fragmentation grenade is somewhere over 200 meters, so the 5/15m "kill/casualty" radius is more along the lines of a guarantee versus possibility. So, a fragmentation grenade has a much larger "danger zone" than a concussion grenade- hence why a fragmentation grenade is considered "defensive" while a concussion grenade is "offensive". Basically, the person throwing a fragmentation grenade needs to be behind cover or he's going to be at risk for being injured by his own grenade. In a historical context, however, concussion grenades were a bit more versatile, because they were essentially a pound of explosive in a convenient package. The Nazis even developed a fragmentation sleeve that could be slipped over the head of their stiehlhandgranates, for extra anti-personnel effectiveness, and used them in "bundles" of six extra heads wrapped around a single grenade as improvised anti-tank weapons. Of course, versatility didn't matter nearly as much as being useful in their primary purpose, so concussion grenades have largely dropped by the wayside, mostly replaced by blocks of plastic explosive such as satchel charges or thermite grenades. While concussion grenades do remain in the US inventory, their versatility has largely been replaced by either 40mm launched grenades, or creative application of C4.
