Does the boss jump regularly? If so, I won't LB since I do not know the timings for the jumps and will not risk a missed LB.

Is it a boss that has a tendency of near-wipe the raid when its on low HP? Something like Diabolos in Dun Scaith? Then I won't LB. Best saved for a Healer LB or the finishing blow. Not to mention using LB on a 24-main raid boss is equivalent to a tickle.

Is it a 24-man raid? I will LB as soon as its up (at 3) unless the above conditions apply.

Is it a dungeon? If I am a caster I will LB if tank is over his/her head with mass pulling and pray that it kills a few of the mobs. I will LB if I am a melee DPS as soon as it hits 3 unless conditions 1 and/or 2 apply. I will not LB as a healer, such a thing should not be needed even if paired with bads.

Is it PvP? Dude, go caster, bind multiple targets in place and let her rip. Have you ever had multiple caster LBs hit while enemies have been bound or heavy? Its glorious!