Golfers used to believe that a draw was hit from rolling the forearms to cause faster face rotation during the moment of impact. With modern measurement, we've seen that this rationale is faulty. The draw is a result of a face that is closed to the path, which causes the ball to curve to right-to-left (for a right handed golfer). The idea of rolling your forearms does make sense from a standpoint of helping keep the path moving out to the right. See why in this video.