Deliverance is a godsend in 8 mans. Something like BisEX that requires you to do as much DPS as fast as possible, you can switch over to Deliverance to help the DPS while you're not actively holding a bird. In The Singularity Reactor, since it's a single tank fight, you can have the WAR drop into Deliverance, put on STR accessories, and go ham on the boss.

Even 4 mans have a place for Deliverance. The final bosses in the Vault and Neverreap summon adds to be killed, while they're invulnerable. Pop on Deliverance, obliterate adds, switch back over to Defiance to hold the boss. You can even use Equilibrium to give yourself back the HP you lose by switching over, so your healer doesn't have to worry about it.