When you reach the impact area, most of your work is done. There is little you can do to change the club path now, unless you jerk your hands in an effort to get a little “extra” from the shot. Your key thought at contact is simply to square up the clubface and hit the ball on its intended line, which you’ve already created with your swing path.
By focusing on swinging through to your target, you minimize any chance of ruining your swing path–and you will hit more solid shots.
When your hands reach the top of your backswing and start down, trying to achieve clubhead speed too quickly causes problems. The result is a violent, jerking motion that throws them off the proper swing path. To start the downswing, let the club “fall” a short way before you add power.