I don't see how they are useful at all, what are they suppose to help in your golf swing?
I think they are just awful for the golf swing.
I think doing exercises on them can help get you in better shape, which WILL help your golf.
Why do you think they are awful?
Learning to swing on a balance disc is awful because you are learning to swing on an unstable surface. A golf swing is very precise and your body learns to use the muscles in a certain way. When you play golf you are swinging on a stable surface not an unstable one. Balance training is good and has its place in fitness but not in trying to perfect a golf swing. To modify your swing to maintain balance on an unstable surface will hurt the performance on a stable surface. The same goes for swinging a heavy club. Your muscles have to be used in a different way than when swinging a regularly weighted golf club. When I was in high school our coaches had the pitchers on the baseball team throwing 1 pound baseballs. The ones that didn't hurt their shoulders became very proficient at throwing one pound baseballs, but not any better when throwing a regular baseball.
You should exercise and train to increase strength, speed, coordination, balance and flexibilty and then use those attributes when practicing your golf swing to better your game.
ADR, I think you guys are missing something here.
All I am saying is I these disks have given me a better sense of how my weight moves in my swing and helps me learn how to control my movements and to be more efficient. If I do something too quickly, jerky, or incorrectly, I lose my balance. If I move smoothly and with a feel for my weight I keep my balance and feel much more efficient. When I move off of the disks the feel is still there for both the bad and the good and if anything, I have a BETTER sense of the ground and how to use it.