Without intending to sound like a spokesperson for the golf industry, it is fair to say that that the advances in golf shaft technology and manufacture have advanced greatly in recent times. Consequently it is useful for golfers to understand some basic information about the various types of shafts that may be fitted to their golf clubs. Using the shafts that suit your swing, especially your swing speed, is of vital importance when it comes to playing the best golf possible.
There's a lot more to shaft fitting than matching swing speed to a S, R, X, or whatever letter is marked.
With Tom Wishon