I think one of the most underrated benefits of training is a better understanding of body awareness. Two things that I always experience with new clients is the inability to activate certain muscles (usually the glutes and/or core muscles) and not being able to understand the relationship of mobility and stability, most notably with segmentation of upper body and lower body.
Why is the ability to activate certain muscles important?
Greg Rose and TPI have gone as far as saying that the glutes are the "King of the Golf Swing." They not only help maintain lower body stability throughout the swing, they help maintain core stability. Having good core stability is important for an efficient energy transfer from the hips to the shoulders.
So the ability to activate these muscles starts with an awareness of where they are and an ability to "turn them on."
Why is the relationship of mobility and stability, most notably with segmentation of upper body and lower body, important?
Being able to keep one body part or segment stable while the other is mobile is a key to power. Think of a sling shot.
If you are holding the sling shot in your left hand, and pulling back in your right hand, there needs to be stability in the left arm and mobility in the right arm. We can have all the mobility in the world, but with out stability, we will not be able to store as much tension between the two for efficient power release. The same goes for the opposite. If I don't have the ability to pull it back all the way (assuming we have the strength to do it as well), then the rock will go nowhere.
In the golf swing, you need to be able to separate upper body from lower body, then lower body from upper body. Having a better body awareness can help.