I haven't unlocked it yet (almost there), so I can't use first-hand judgment or experience on this one. I would think, though, it would be useful when you're in a party that needs you for full heals but also needs just a few ticks more of DPS to truly be efficient. When your party is lacking on the DPS side, every little extra bit you can get from the healer is helpful, even if it's not in Cleric's Stance. As easy as it is to switch back and forth from Cleric's, if the party is doing okay on heals, the healer shouldn't be afraid to pop Cleric's and help DPS, if the situation allows and then go back to heals as usual.