If you look on your saddle pad it might have velcro strips on it, it think they are actually to go over where the girth is, but they are long enough to go around your wrists.
They are velcro so will come undone if you move your hands up with you when you post. (and will not hold you if safety is a concern) - the instructor who recommended this was a GP dressage rider.
I have a bad shoulder though and didnt feel comfortable with where this put my hands (it was slightly lower than normal) so I she then had me hold the monkey grip instead.
Mainly its just something to make you aware of where your hands are. My hands don't move anymore because I spent months holding something
before I rode normally - it is just a matter of overriding what your muscles have been trained to do. When I recently changed riding places (because I moved) my new instructor commented that I had nice stable hands
Made the months worth it
Hope that made sense