You're Correct!

During the golf swing you will basically swing the club head in a direction parallel to your shoulder line.

Following this, if you set up with your shoulders aligned parallel to the target line, then it makes it much easier for you to swing the club head along the target line as you begin your back swing and it also makes it much easier to swing the club head along the target through impact.

The direction that the club head is travelling in as it impacts with the ball, or your swing path, influences the accuracy of your golf shot and the type of shot that you see produced. With the club head travelling straight along the target line and with the club face aiming straight down the target line, you will produce a straight and highly accurate golf shot.

Its absolutely crucial to have your shoulders aligned correctly as you swing the club head parallel to this alignment and this influences the direction that you will hit the ball in.

The correct position for your shoulders to be in during the address position is parallel left to the target line. Your shoulders are parallel to the target line but as you stand away from the target line your shoulders will be parallel to the target line but left of the target – parallel left. You can check your address position shoulder alignment by placing a club across your toes (this should be parallel and left of the target line for right handed golfers) and then placing a club across your shoulders and chest. Notice if the club across the front of your shoulders is parallel to the club across your toe line. If its not parallel to the club across your toe line you can now adjust your shoulder position until it is and then look up at the target to get a feel for the difference with this new and improved position.

If you set up with your shoulders aiming right of target, then as you swing the club head away from the golf ball, the club head will be travelling on the inside of the target line. As you swing the club head back down towards the ball it will return back to the golf ball from the inside of the target line, then strike the ball and continue to travel across the target line to the outside. This produces and in to out swing path and if the club face is square to this swing path you will now produce a golf shot that flies straight, but to the right of the target, or a push.

If your shoulders are aligned to the left of the target at set up, they are open. You are now more likely to swing the club head away from the ball on the outside of the target line and as you return the club head back down towards the ball, it will be travelling from the outside of the target line to the inside, or parallel to your shoulder alignment. With a club face square to this swing path you will now hit a straight shot left of target. With your club face aiming right of this swing path, you will hit a shot that curves to the right in the air.

Shoulder alignment can greatly influence swing path direction which in turn can influence the direction of flight and spin imparted on the golf ball. Focus on a good, square shoulder alignment in the set up phase in order to improve your golf shot direction.