I run a PvP Arms Warrior and a Disc Priest (currently sidelined) and I'm all for having a Disc Priest with me. PW: Shield, PW: Barrier, Pain Suppression, crit heal bubbles, Dispel Magic, Fort, PoM, Shadow Protection, Psychic Scream, Inspiration, Leap of Faith, and Shield damage reflection. All I have to do is swap to sword and board, go defensive, and I'm golden from flag room to flag room between all of our cooldowns.