Sgt. Rory Miller points out that fine motor control is highly unlikely to work in a high stress situation because the hormone cocktail released into our system shuts down fine motor control.
One useful way to think about internal martial arts is that we want to make our movement routines utilize gross motor control only. Even the feet must be loose and floppy, as if your legs had become like jello from shaking.
Grabbing is one of those movements which could be fine motor or could be gross motor.
It’s important to teach people not to grab too much.
First, grabbing is often defensive. It is done to limit the other persons movement. This kind of thinking puts you at a distinct disadvantage because your opponent is now free to hit you. Of course it can work, especially if your grab is truly disabling, like a grab of the neck, or a grab with “bone crushing force,” or a quick yank intended to dislocate a joint. Smaller people grabbing larger people doesn’t seem like a very good idea though.
The Second reason not to grab is that the center of the palm is supremely insensitive. If someone touches my arm with their palm they simply won’t feel the punch coming. Touching with the palm is usually defensive and ineffective. Striking with the palm is a different story. You don’t really need sensitivity when you are striking.
We tend to think of gross motor control as being insensitive but it is not. Gross motor movement is just one big mass of sensitivity, the way babies move. In that sense fine motor control is less sensitive because it effectively shuts out whole body movement in favor of local control and precision.
UPDATE: I had a video here showing another teacher using palms in push-hands but I removed it because I couldn't think of anything nice to say and in all fairness each teacher should have the opportunity to explain their methods before being judged, even on youtube!