One when doing a theatre workshop where we put on 12th Night after a week of rehearsal, the cupped hand was a trick I used in the first run thru to differentiate me from the other characters, and the director liked it so much he insisted I keep it.

It's very useful - it helped someone who had been told by the school 'music teacher' - or that was his pay slip title, that 'she would NEVER sing' - she tried it to listen to herself and improved massively, being able to hold pitch etc after a few weeks using it.

Not much of a 'teacher' I suppose.... :-)