During your golf swing, the club head should be at its fastest as it swings through impact with the golf ball.
If you accelerate at the bottom of your golf swing and deliver maximum club head speed to the ball, then you will hit your longest golf shots. Swinging and accelerating too early on your downswing will result in the club head reaching its fastest speed before impact with the golf ball and therefore you will be decelerating as you hit and not achieving the distance that you could. Timing the fastest club head speed to be when you are striking the golf ball is really crucial for maximum shot distance.
Try the following drill to see if you are accelerating at the bottom of your golf swing for maximum shot distance. Take up your golf stance. Now turn the club the other way around and hold the shaft of the club nearest to the head end with the correct grip. Swing the club back and through and listen for a 'whoosh' sound as the club swings through the ball. If you do not hear any noise, work on swinging faster until you do hear it. Then listen to where exactly you hear it. Is it before the club would connect with the ball or is it where the club head would be connecting with the ball?
You should hear the 'whoosh' where the club head would connect with the ball as the whoosh is produced where the club is moving most quickly. Make a few swings, altering where you hear the whoosh, until you are hearing it where the club would be connecting with the golf ball.
Get the feeling of this and then turn your golf club back the usual way around and play your golf shot with the 'whoosh' in the correct place so that you are accelerating at the bottom of your golf swing for maximum shot distance.