More important than all that is the fact a party SHARES the same Limit Break, so if you use it the whole parties limit gauge is emptied.
It is typically used to burn down a enemies or group of enemies in a fight that can be a issue if the target is not killed fast enough, a healer may also use it to try save a wipe...like a last resort.
It isnt something you blow on some trash mobs thinking its YOUR limit break, its a group limit break.