I saw an electrician use one for troubleshooting. Half the outlets in the house were in serial on the same circuit, and there was a problem in the wall somewhere. He disconnected the wires from the breaker and backfed power from a live circuit to an outlet to see if there were any more breaks further away.

deleted by creator

Except for the surgeon who performed a self-appendectomy, they probably go to a different hospital to avoid gossip.