well, it depends on more than one condition and that is more than a group of randoms can handle, despite being very easy to determine:

I play mosty melee, almost always monk.

First, when LB is ready and I am in my busrst phase, doing LB is a waste of cooldowns. that's why I hate all those "USE LB NOW <se.1>" macros, because there is time when LB fits into my rotation and time when it is not. If the LB had 2s cast (including animation lock) and was affected with buffs, OK, but it is not.

Second, if I have a ranged/caster in dungeon, using LB on trash pull is better. But LB is usually charged during 2nd boss, so I don't use it because I hope for AoE LB next pull. If the caster won't use it, well, can't go back in time...

Third, a lot of dps think you have to kill boss with LB or the Earth will explode. By the time we reach last boss you should get the feeling on how fast the boss will die, so: if it takes too long, wait for LB2 (makes more damage) or LB1 right after opener (or when it is ready and you are not in burst phase), because if LB2 is not taking away at least 10% you may just as well not use it.

All of this is hard to communicate in PUG, especially in DF, despite being a common sense. You have to trust 3 strangers to have common sense: that is why LB is not used very often.