Most high handicapped golfers allow the left heel to lift off the ground as they make a back swing movement simply because it makes it easier to complete a "full back swing

However, a back swing movement that is carried out whilst keeping the heel of the left foot firmly on the ground builds up the torsion of the muscles to their maximum with a shorter back swing movement. In addition, it will also result in the ball going further and with better control.

 

By keeping the heel firmly on the ground, it allows you to consistently achieve the maximum amount of torsion within the muscles of the body every time you perform a full back swing movement, subsequently this gives the golfer a consistent level of energy to expend as the down swing movement is performed, thus allowing the golfer to accurately predict the distances the ball will fly through the air for any particular golf club.

But in addition, by keeping the left foot firmly on the ground also restricts the swaying effect of the upper body as the back swing movement is performed.

So if you wish to have a consistent back swing movement, you must not allow the heel of the left foot to lift off the ground.

Right Foot.
In addition, during the down swing movement, you must not allow the heel of the right foot to lift off the ground until the precise moment the club head strikes the ball.

You must keep both feet firmly on the ground throughout the back swing and the down swing movement,