I teach to have the throwing hand behind the glove. I have found that having it there significantly reduces the time it takes to get the ball of of the glove when throwing. When the ball hits the glove, the glove is rotated 180 degrees to face the catchers and the throwing hand is right there ready to grab the ball and lift it out of the glove.
As far as blocking goes I teach to send the hands to the ball and then have the body go to the hands. I send both of my hands together to the ball then all I am doing with my body is driving towards my hands and recentering myself on my already established new midpoint. That new midpoint is the location of my hands. I do not have to teach myself to recenter my midpoint on my hands, that is something we all do natuaraly. This cannot be done nearly as effectively if the hands are not traveling together.