Golf is a target orientated sport. We stand an awfully long way from the hole and have a very small target to aim for, therefore accuracy with each and every golf shot should be our first consideration when we set up to the golf ball.
A square to target club face is preferred to produce straight golf shots, as when it is used in conjunction with a square swing path, the ball is impacted with a minimal amount of tilted backspin, which is more commonly referred to as side spin. If a ball is able to fly through the air with backspin which is rotating on its axis, and not tilted backspin/side spin, this will allow the golf ball to fly straighter, towards the target.
If the club face is impacting the ball and is not square or pointed towards the target, it can only be done so with a corresponding none square swing path. This would produce an amount of curve spin on the golf ball, which can be difficult to control on a consistent basis.
If you learn to hit the ball with a square club face, improvements to the accuracy of your shots will be easy to see.