On my computerized machines, the cord comes right out of my machine- no hazzle at all - zip, it's unplugged.
I do it not so much to save my fingers, but to save a very expensive repair charge if it accidently started when I was cleaning. When I clean the bobbin area of lint, I take the throat plate off and clean the whole area of lint around the feed dogs, everywhere. On the mechanical mechines I then go ahead and oil them according to my instruction manuals. I think cleaning them of lint with them connected would be a lot like changing the oil in your car with the engine running. wouldn't think of doing it for lots of reasons.