I've said this before, but not in this thread: in a small gathering, when a singer cups his hand around his cheek or ear, this may well hide his face and muffle his voice for some of his audience. So although the singer may hear his own voice better, the others present may not appreciate not being able to see his mouth or hear the words clearly because of the arm/elbow in the way.

It's not about the singer makiing a beautiful sound to wallow in, it's about communicating the song to other people. The singer needs to consider whether a hand to the ear or cheek is going to enhance or impair communication.

It may be helpful in a recording studio, or in a massively amplfied concert, but that's not the context most of us are used to.

It shouldn't be necessary just because you're singing harmony - the whole point it to hear the other singers and blend with them. Choirs, whether professional or amateur, don't stand with their arms to their faces - they learn to listen to the other parts, including the orchestra, and sing in tune with the rest.

Marje