My main is Monk/Dragoon.

I have done many times Brayflox like many of you guys and got in 2 different groups. If its a fast group I wont use LB till the last boss , dont wanna risk not having no LB for the last boss. In slow group I use it also on the second boss.
Always on the last boss they start to scream LB on 20% , dont ask me why. I always use it when he almost start to drive away , but that also depends how low he is. For some reason i cannot move for 3-4 seconds after a LB so I always use it at this stage ( EU player ).

The only thing that irrited me are people screaming LB in Titan Hard/Extreem. Yes , some tanks screams at melee too kill both adds with a Melee LB in extreem. But in Titan hard you see people scream LB when they are dead and dont know the rotation themselfs. Sorry , i am not going to use a LB before the landslides or plumes come.