The shoulder turn will help you to increase your backswing therefore giving you the possibility for more distance.

The Stretching Drill:

The bigger the radius, the bigger the arc of your swing and the farther the ball will go with less effort. How do we promote a bigger arc in your swing?

Answer: Improving the turning of your shoulders.

The muscles in your back may not be stretched enough to create the bigger arc that you need to play to your potential. If this is the case, practice this exercise many times a day for a few weeks. The stretching of the muscles in your back will enable you to keep that left arm straighter therefore maintaining the radius of your swing.

To improve the turning of your shoulders, practice these exercises:

With your right hand behind the left arm, pull the arm across the body causing the shoulder to turn therefore creating a stretch in the upper left side of the body.

This will also help the left arm to remain extended during the backswing.