Limit Breaks

[Estellios]

For most dungeons, it's reserved for a melee DPS first, if not that then a caster. Typically people just use them for big damage on a boss but none of the dungeons pre-50 require them for anything. There are some exceptions, most notably bosses that have add phases where a caster LB can clear them all in one shot. If you think the healer LB is needed and can prevent a wipe, I'd say go for it.

Endgame stuff is typically structured around using specific limit breaks at specific moments, so it's a different dynamic there.

Edit: For the above poster, the tank LB is extremely useful in the Ultima Weapon hard mode fight where the group needs to eat consecutive bursts of damage that would otherwise kill a few people. I have also used it to save a Titan Hard mode run when both healers were dead, Titan was at a sliver of health, and he was about to do his stomps. Doing the tank limit break there made the stomps leave the DPS with about half health instead of outright killing them which allowed us to get the win.