You use it in place of a Thrash, on average once every cycle, when Wither and Shock are on cooldown and you don't yet have 3 stacks of HD. It does have a slightly lower chance to proc Energize, but it doesn't make an appreciable difference in overall self-heal timing while simultaneously doing a lot more damage.
Good point, i did not realize it could proc energize. Guess I'll have to move my abilities around slightly. Was hoping to avoid using another proc'd move lol.