Here's an off the wall thought, maybe it has nothing to do with punching technique at all, maybe it's simply a way to build reflexes, timing, etc in a very convenient way. As long as you don't get it in your head that that's how to throw a punch then it's fine. I do stuff all day that doesn't mirror punching at all but it doesn't hurt anything.
_________________________
Member of DaJoGen MMA school under Dave Hagen and Team Chaos fight team under Denver Mangiyatan and Chris Toquero, ran out of Zanshin Martial Arts in Salem Oregon: http://www.zanshinarts.org/Home.aspx,