I was under the impression that in raids, you generally want to save LB3 to use during add phases unless using it ASAP will allow you to get a second melee LB3 off over the course of a fight.

Though as far as SB goes, outside of it being virtually required for the OS3 add phase, it's only applicable for the OS7 Bibliotaph or during the Shinryu Extreme burn phase to nuke both of his wings.

As far as dungeons go, it's most time efficient to use a caster LB to blow up a big pull of 5+ enemies. Otherwise, saving it for a melee LB2 on the final boss is probably ideal.