Okay, so there the limit break button. Got it. Does big boom... whatever. I've been yelled at for not using it because I'm still not used to it.
"How'd you get to such a high level without using limit break?!"
Dude, relax. It took me a week to reach this level. It's not like I spent a few months working at it. It took a week. I still have that newbie symbol next to my name because I don't have enough playtime.
Anyway, I decided to google this ability and find out what all the fuss was about. This didn't help, however, because I found even more confusion. Post after post after post of varying opinions on when it should be used and by whom. Casters get yelled at when it should have been the Melee or Melee getting yelled at because the caster should have done it; or first boss vs the last boss, etc...
I found several posts by DPS stating that they just stopped using it until they're told because they got tired of tanks yelling at them for wasting it. It's the whole damned if you do and damned if you don't type thing.