I've never understood why this is even a teach. What difference does it make? What is the purpose? From my experience with the kids I instruct, if you don't tell them any different, they show the ball to 3B (RHP) in a nuetral, natural and stress-free position. The kids who show the ball somewhere else have been told to, but not one has been able to give me a reason why.
When I consciously show the ball to 2B the muscles in my forearm contract, right before accelerating my arm, the last thing I want to do is create stress in my forearm.