The moment of truth in the golf swing is at impact, the moment the club-head meets the golf ball. This is when the result of your shot is decided.
Nothing else matters at this moment. It does not matter whether you have an upright or a flat golf swing. It does not matter if you have a swing path that is inside/out or outside/in. It does not matter whether you use an overlap grip or an interlocking one. It does not matter if you prefer a forward ball position or a rear one. It does not matter if you set up open to the target or closed to it.
All good players have this one thing in common. At impact the left arm (for a right handed golfer) is fully extended and the left wrist is in line with the forearm. This is frequently called a flat left wrist at impact.
History shows us great golfers with very unique looking golf swings. Arnold Palmer with his lashing attack at the golf ball resulting in a lunging look at the finish. Look at Jack Nicklaus with his upright back-swing and big leg drive on the down-swing. Gary Player putting his all into every shot in which he would actually take a step forward after the shot. Jim Furyck has his unique up and out back-swing, and then re-routing the club to come from the inside path to strike the golf ball.
They all get to impact with the left arm solid and the left wrist solid.
Most amateurs arrive at impact with their left arm and wrist broken down and in a collapsed position.
There are many reasons this happens, but one of the biggest is the false impression that the golf ball must be scooped or lifted into the air. This type of hitting action causes the breakdown of the left arm and wrist.
What you really want to do is hit through the golf ball, much as you might swing through a baseball or a tennis ball, with no thought of trying to lift the ball up. The design of the golf club will cause the ball to lift.
Here is a drill to help you feel the correct impact. Stand next to an object you can strike such as a punching bag or an upholstered chair. Assume your golf stance. Swing your left arm away from the object, and then swing at it feeling your left arm and wrist straight at impact. You can view this drill and correct and incorrect impact positions on my website www.golflessonsorangecounty.com.
Improving this key principle is the secret to vastly improving your golf game.