I don’t see flat lie angles as something you have to do. Obviously there have been some great player who played the game off more upright gear. Nicklaus did. Moe did because of his unique approach. Hale Irwin comes to mind.
But as far as flat lie angles… I see this as stacking the odds or loading the dice in your favor from a purely geometric standpoint.
The main theory is that the flatter you swing, the more the results of OTT become nullified.
What does OTT do? For better players it often means a hard pull shot long and left. Which for right handed golfers is usually the worst place to miss a green. Trevino talked about this in his book, and the reason he felt he could beat Nicklaus. He believed Jack’s wedges and short irons were too upright, and Jack would often leave himself left to right downhill putts.
It’s instinctive to want to come a little OTT especially with the short irons to hit the ball crisply, not fat. For most golf swings, this is going to shut down the face or take loft off, and pull the ball.
Try this… how far left can you pull a shot offline with an upright 8 iron? I can easily come OTT and hit it more than 45 degrees left of my original intented flight path in an extreme display of butchery. Now tee up a driver and hit a shot off your knees. Assuming you can make contact, there is no way you are going the be capable of starting a ball that far left.
The other advantages of flat lie angles are that they naturally put the club more behind us. This tends to engage our body in a more natural way than if the arms go up over our head… and oddly enough requires less dropping into the slot than an upright swing… because to some degree, you are already there. The flatter plane also promotes clubface rotation in a more natural way, and tends to stablize lowpoint also due to the more sweeping motion of a flatter swing. I don’t find myself taking the big deep divots I used to and contact is much more ball related than ground related.
There are other concepts too, such as lowering your center of gravity to stabilize the golf swing and how flatter planes encourage better ground pressure loading… better access to the 4:30 line and so on. I don’t think it’s a mystery that Hogan, Nelson, Trevino, Knudson, DeVicenzo and so many others played off flat platforms. During my playing days, three of the Order of Merit winners on the Canadian Tour (Guy Boros, Jim Benepe, Bob Panasak) all swung very flat planes. I played with Bob Shearer in Austalia who was a great flusher, and Peter Senior of course, very flat action.
I can also speak from my own personal experience going from an upright swinger to a flat hitter how much easier golf is now with the ball striking.
Keeping this on topic… do baseball hitters prefer a pitch coming across their sternum or down low at the knees and why? I’m not much of a baseball expert, but I think the high pitch is a dangerous one to throw at a power hitter?