Certainly I was taught (by our maintenance man) to give it a time on left, then back to both, then to right, then to both, stopping at each for while. That has more than once revealed an oiled-up plug where I suspect we wouldn't have noticed otherwise.
Turning both mags OFF is likely to wake up the neighbours with the BANG when you turn back on. It would be an absolute no-no for a car, but probably isn't quite as disastrous for an aircraft. Still wouldn't do it.