You don't hit the ball over the center of the plate (as traditional batting tees suggest). You make contact in front of the plate. But there are two other equally important reasons to use a forward arm design:

• The forward arm eliminates "dipping" or dropping the hands and trailing shoulder to lift the ball with a "looping" type swing. If you "dip" with the AST, you hit the back of the arm. It forces you to take the bat straight down to the ball, leveling the swing at the point of contact. 
• The forward arm also pivots and rotates to place the ball on the inside or outside of the strike zone. Then, the arm points in the direction to drive the ball based on pitch location (i.e. pull the inside pitch, go with the outside pitch to the opposite field . . . "Hit the ball where it's pitched").
• The AST can be assembled or disassembled, by hand, for easy storage and transportation. And, it uses a hollow, canteen style base that is filled with sand or water (and sealed with a rubber plug). When filled, the base provides weight for stability and when empty, the base is light and portable.    
• BATTING TEE ONLY