Wow, thought I was in the WoW forums for a second. Anyways, if you're progressing on a fight, saving LB3 to see more of the fight is pretty much the smartest use of LB. While it's "optimal" in a vague sense to use melee LB3 in a single target boss, during any type of progression it's almost never practical to pop LB3 randomly. Furthermore, in Shinryu or Shinryu EX, it's suboptimal to use melee LB3 on the boss. It is far more effective to use it on the adds if your DPS tanked the floor a bunch and you think you'll die to protostar, or to use it on his wings at the end of the fight in Shinryu EX. It's also disingenuous to say that in "almost every fight" melee LB3 is optimal, since the majority of fights in the game are trash mobs, and if you have the ability to LB at all, it's more effective to use caster or ranged LB during those fights.