What you should NOT do is called casting.
Casting is a sign of a premature release of the 90 degree angle. It will reduce the ability to develop club head speed therefore, causing loss of distance. It indicates the right side over powering the left at the impact zone causing a lack of club head speed.
The 90 Degree Drill (what you should do):
Try this drill and see the improvement in your motion. By allowing the right hand to separate during the downswing you can see how the 90 degree angle is maintained. Let the hands come together again as the club head approaches the impact zone. Practice often for your body to remember the correct motion.
Maintaining the radius of the left arm will help prevent the premature release of the right hand.
You can hold the club near the middle of the shaft with the right hand in order to reinforce the feeling of the 90 degree angle.
Bring the club back until your left arm reaches about the 9 o’clock position. A 90 degree angle should be created between your left arm and shaft.
Keep the right hand in this position as you pull down with your left arm maintaining the 90 degree angle until your left hand approaches the right thigh. Gradually slide your right hand closer to the left as you repeat this drill until your hands are in the normal grip position.
Practice this drill often and you should see an increase in your club head speed and distance with your shots.