Suppose you are in Titan HM Phase 5 as a DRG. You have 3 members dead like you said, and you decide to hold off on the LB3. Realistically speaking, what are the odds that a healer will be able to ress all 3 dead members (who may have even been landslided). Are you going to hold off on a Limit Break that just got to Level 3 somehow hoping that healers will be able to resurrect people?

I'm asking you this because I was faced with a similar case yesterday (half the group was dead), and I used my Lv 3 LB and it even allowed me to pull off a Lv 1 to finish off the fight. When it is strategically viable to use an LB then yes, you should use it then (Garuda, Ifrit, Ultima), but hesitating and overthinking a chance to pull off an LB more times than not just leaves it sitting there while it could have been used.