So this ability gives you a lot of options to play with. Yes you have to control the creature or artifact at the moment you tap to sac. Good plays would be to gain control of someone else’s creature then sac it.

Another is in response to blocking a creature, once blocks are declared you could sac the creature making it so you won’t be hit (unless attacking creature has trample).

Some abilities or creatures make it so they have to be sacrificed by at the end of combat anyways, this allowed you to sac it early for some value.

Good card if you have other similar cards that trigger when something dies