In HM Ifrit you get to use 3 of the 4 in 1 fight. Wait for the nails, BLM or SMN casts Doomsday, This usually does enough damage to put the LB bar back to ~2 full bars by the time Hellfire goes off. Once it does, use the Healer 2 bar limit, just as the fire covers the screen, for instant party heal. Then, you usually get to use the melee DPS 3 bar limit sometime after that as well. The only LB you don't see in that fight, if done properly, is the Tank LB.