I think it boils down to the standard you play.
Some people point blank refuse to back up.
I back up if the game situation requires it. If we are batting out for a draw I am often next to the umpire. However, if there is a game on I am 1/3 of the way down by the time the shot is played, I am always ready to turn and dive back in if required, but more often than not am looking for the single every ball.
I too use the screaming YES formula, very effective.
When facing, I like to see my partner backing up as I know then there is the chance for quick singles. One thing I cant stand is the non-facer calling for me.