This is a PvP spell mostly. Think about it like that:
You're healer priest, arena situation, you're hiding and LoS, 3x3, destruction warlock almost one-shots your rogue and Ding-you're swapping the health, and going to column to heal yourself.
As a Shadow Priest, it will be the same from PvE PVP perspective:Swap the health-Dispersion-Bingo.
The thing is, if the latency and well-played team will allow you to do that. For Arena, that level of cooperation is required. For PvE, however it should be a special occasion(something like your own Lay of Hands, however a bit complex one)