Amateur golfers that hit up on their irons are robbing themselves of distance and accuracy. Why? Because the golf club is designed to strike the ball as it is still moving downward. This achieves the desired compression and spin, which keeps the ball in the air for longer.
In this video tip from TG Elite Pro Chris Ryan, he demonstrates a drill that reinforces the correct angle of attack you need to have on your iron shots to hit the ball longer and straighter.