How many times have you seen something similar to this in your local gym; the guy who is to tight to squat properly drops squatting from his programming all together (usually replacing it with more sets of bench press). Conversely, the hyper mobile woman taking another yoga class instead of hitting the free weights, and becoming yet more flexible.
“Just because you like doing it – doesn’t mean its good for you”
Dr Greg Rose, Titleist Performance Institute.
Chances are the girl taking the yoga class already possess adequate joint mobility to perform the golf swing. However (like most women actually) stability and strength are likely limited, indeed a lack of strength and stability are likely to be the limiting factors to golf performance. For this individual improving in these areas will have a much a greater effect on performance than further increasing flexibility. Similarly the strong, tight guy has plenty enough strength, stability and power but lacks the mobility to fully exploit this within the range of motion of the golf swing. A yoga class or two, some pilates, or introducing some dedicated mobilisation work is likely to do a lot more for this individual than adding another 10kg to his bench press PR.
The moral of the story is, honestly determine your strengths and weaknesses are (or better yet have a qualified professional do it for you!) and then attack them in the gym. Don’t just perform exercises that you are good at or that you like, they are probably the last ones your body really needs!