I always turns the mains off, ever since I did some work and the wiring had been reversed!
I have rewired most of this house (many years ago) and so far it has passed the tests each time - new kitchen, bathroom, c. heating - quite surprised actually. Everything was a complete mess when we bought the place.
Mind you, when the floorboards were up, I spent more time trying to extract the moggies from underneath than I did re-wiring.