When I first started racing bikes I had a shallow drop bar. I ended up with painful bruises just above my wrists from all the pulling on the bars. With the shallow drop my wrists were always in contact with the bars when out of the saddle and sprinting. Deep drops provided more room and a better angle from elbow to hands. This eliminated the wrist contact points. I pulled on the bars with my hands with minimal wrist or forearm contact. Huge improvement in comfort.