Im having a hard time finding ANY use for power bash. Is it completely useless?

A power attack staggers more, costs LESS stamina, and deals TONS of damage.

I'm having a hard time knowing how to do a Power Bash. I was mucking about with a Mudcrab the other night, levelling up my Conjuration, Light Armour, Block and Restoration, and having never really used a Shield much I decided to get the Power Bash Perk. When I was done with the Mudcrab I did just that...Power Bashed him about 50 feet. Was great. Since then I've tried Power Bashing again, but it doesn't seem to work. Does it only activate when you're about to kill someone, i.e. is it basically a Kill-Cam type move?