I won't ask someone to do something which I wouldn't be willing to do if I was in their position.

Exactly what I was going to say. Also, ideally a supervisor knows how to do all the subordinates' tasks, and can jump in and help when necessary... but sometimes you hire an expert to do an expert's job. A supervisor does not need to be able to type 120 wpm in order to supervise a transcriptionist who does.