From this dynamic position, your body is ready to quickly move in any direction. If your weight falls on your toes, the clubhead will tend to start outside the target line. If your weight rests on your heels, the path will tend to be too inside. Neither path is conducive to generating much clubhead speed or consistent contact. It's imperative to maintain a good right knee flex.
Many golfers lose their balance because of tension in their legs.
They tighten their knees, which forces the right knee to straighten at the top of the backswing, leading to a reverse-pivot. At the top of the backswing, your balance point is over the middle of your right foot. If it is, you should be able to lift your left leg completely off the ground and hold the position to a count of three, without wavering. On the follow-through, the swing's momentum should carry you to a full, balanced position, with almost all of your weight over your left foot. As your upper body unwinds, your shoulders should finish over your left leg, almost at a right angle to the leg.