Besides being an immediate fix for ankle dorsiflexion, this method forces the lifter to use very strict form. Any kipping, shifting, jerking, or wiggling will literally launch the weight off the feet.
In addition, activating the feet and ankles increases tightness and stability throughout the entire body through a neurophysiological phenomenon known as "concurrent activation potentiation." This is just a fancy term describing a state where every muscle in the body from head to toe is activated so fiercely that neural drive is increased to the primary muscles, thereby enhancing force production.
As a bonus, this technique eliminates energy leaks as there's no weak link in the body.