left hand in control and right just along for the ride. if the right hand is in control you swing back faster and the right arm and hand are in control on the downswing. you want the left to control the downswing.

try swinging back with the left hand and arm in control and count, then do same but take away more with the right hand and you will see you swing faster and have less control. .2 to .4 of a second faster.
bill