Many club golfers kick start their swing incorrectly by swinging the club back on either of two incorrect swing paths – that is whipping the club too far inside the target line or letting the club drift outside the line.   These are the only takeaway faults you can make and they are a major contributor to hitting poor shots because if your takeaway path is not straight, or on the correct path, this then sets in motion a chain of events where your downswing and through-impact positions mirror what occurred in the takeaway.  The degree in which the club is out of an ideal path is reflected in the severity of the mis-hit.  For example, if you take the club away on a path well inside the target line, the club shaft and head, in the majority of cases, then approach the ball from way inside the line.  The swing path through impact is then very much an inside-the-target-line-to-outside-the-target line.

Conversely, if the shaft points outside the target line in the takeaway, it will follow this same outside-the-line path back to the ball and you will have no recourse but to swing across the line of the ball to have the club finish inside the target line in the follow-through. When you set up to the ball, it is sitting on the target line.

The path is never going straight through, it is always on a slightly curved path.  How does this happen?  If your body turns correctly, that is it rotates or turns in a circle, the club will follow a correct path.  Imagine you had dangling rope-like arms when you swing the club.  This loose feeling in the arms allows the body to control the path of the club, not your arms.   For the vast majority of golfers, who slice the ball as a result of a swing path that moves from outside the target line to inside the target line through impact, the tension in their arms and hands can create the incorrect sequence and therefor a poor result.

Source Golf Australia Peter Knight