The weighted ball routine is one of my favorite speed builders!  The heavy ball adds extra resistance making the pitcher work harder through the arm circle.  When followed with the light weight ball, she under-loads the arm, allowing for greater arm speed and increased ball speed.  I incorporate the weighted ball into many other drills (knee drills, long distance, pitch under right leg, and behind the back snaps) for added resistance.  The set comes with the 11 speed building drills I recommend.