The role of the backswing is purely to build power in the golf swing.
However, the simpler the backswing, the simpler the downswing will be to deliver the golf club to the ball and so the more consistent the shot will be. Use this exercise to simplify the backswing by connecting the arms and shoulders together for improved timing and a better connection with the ball.
The backswing is dominated by an upper body turn that winds up against the lower body. The shoulders power the swing and should turn backwards so that the golfer's back faces the target. At this point, the arms should still be connected to the body and so the hands should be positioned directly opposite the golfer's chest. The relationship between hands, chest and shoulder turn is important and all should stay together and be connected through the whole swing for consistency. The problem for many golfers is knowing when to stop the turn back and begin the turn down. As soon as the shoulders stop turning back, they have reached their maximum limit of rotation and the backswing should not continue any further.
At this point, the golf swing is connected as the shoulders, arms and hands are all working and moving together as one unit. Here, there is nothing more to be gained from going any further, although the golfer may carry on with the arms and hands moving them higher than they should as it feels like more power will be gained. If the shoulders stop but the arms, hands and club continue moving, the swing loses it's connection and the downswing becomes a recovery motion as the golfer tries to regain connection for an effective impact position with the golf ball. This costs the golfer consistency as sometimes the connection will be recovered and sometimes it will not.
Here is an exercise to time the backswing well and maintain the connection between the arms and shoulders.
For this exercise, there needs to be an awareness of the front arm and front shoulder (left for right handed golfers and right for left handed golfers). They should stay together as one unit in the backswing motion. Take a slow backswing and note when the shoulders stop moving. When they do, concentrate on stopping the arms at the same point. The front arm should be approximately 90 degrees to the line of the shoulders. To help with stopping at this point, hold the position at the finish of the backswing movement and note an object in the background that the front arm points at (a certain tree or light on the driving range, for example) or imagine the arm as the hour hand on a clock face and what number it would be pointing at (10 o’clock for instance). With each practice swing, make sure that the arm in the backswing only ever reaches this point but also make sure that the swing is only powered by the shoulders.
This exercise provides a simpler and more connected swing for consistency.