A great way for a post player to add value to their game, is to be able to score out of the high post area. The reason why is because most post defenders are not as comfortable guarding the ball out away from the basket. This type of scoring situation works really well for post players that have good footwork, and a quickness advantage over their defender.
The reason that the post player is going to work on flashing up from the block to get the catch, is because this will keep the post defender from pushing them out to the three point line on the catch. Great post players are able to read their defender and then make the correct move. That is why for this post move drill you are going to work on several different moves. This will allow the player to evaluate the defender on the catch, and then make the appropriate move to exploit them.