A regular customer of mine called, and asked for a receptacle added- right where ther was a blank cover on the wall would be fine!
(This office often has unused boxes in the walls, stubbed out to above the ceiling, originally installed as future phone/data points. As you might guess, I have used a few of them for new receptacles- it doesn't get any easier than that!)

When I took off the plate, I was surprised to find a run of EMT- with operational circuits in it- passing right through the box.