The correct transfer of body weight in the golf swing is imperative to achieve a proper stroke on the ball. It must be learned early on because the natural tendency for most people is to transfer the weight incorrectly, usually in the exact opposite fashion of the proper method (resulting in the classic 'reverse pivot', which will usually translate to weak, over the top slices). The longer that one performs the incorrect motion the more difficult it will be to unlearn it.
Simply put, for a full swing, when the club comes back, the body weight should come back to the right side (for right handed golfers). The golfer should feel as though their body weight is 'loading up' on the right side as the club comes back away from the ball. Do not let the body weight 'roll' to the outside of the right foot, because this will cause a sway away from the ball, and the head and spine will not remain still (imperative for making good contact). Rather, feel as though the body weight is loading up on the inside of the right leg and instep of the right foot. This will serve as a solid 'post' to pivot back on instead of a weak and passive one.
When the club reaches the top of the backswing, the golfer's first move should be to turn their hips to the left, quickly. Then the golfer should effort to get their body weight over to the left side quickly as the arms and club follow. The left leg should remain firm and solid so that the golfer can powerfully thrust their body weight to the left side without the leg breaking down or falling out of balance. At the end of the swing, or the follow through, about ninety percent of the golfer's body weight should have transferred over to the left side as they face the target and hold the finish. The right heel should have come up and it should feel as though it is very easy to lift the right foot because all body weight is on the left side of the body.
So, why don't people do this naturally? Generally because the beginning golfer feels the need to try and help the ball into the air rather than trusting the loft of the club to do this. What this creates is a 'scooping' motion where the golfer leans into their left side on the takeaway, with the spine tilting forward as the club comes back. Then on the downswing they transfer their weight to the back foot as the club comes down and their spine tilts to the right, trying to make good contact on the ball (usually unsuccessfully) and often actually walking or falling backwards on the follow through.
Think of it like this, would you rather have your body weight transferring forward, through the ball (to the left) as the club makes contact, or away from the ball (to the right)? Obviously, more power will be imparted on the ball (and better contact/ ball flight) when the body weight is helping, rather than hurting.
