1. Off-Heals: If a healer would happen to go down, it may be in the best interest of the group for a DPS to throw some off-heals for a bit until the healer is rezzed.
And continue for a few seconds after the healer is up, since they will rez with little health, or energy, or both.
Additionally, if a DPS has off heals, they also have a combat rez, and it should be they, NOT the other healer, that does the rez. It should be done immediately, and without being asked to do so.
EDIT: combat rez is also for boss fights only, not trash pulls.