There are supporting arguements for both sides of this. In doing my own research I have found that it is a waste of money and simply is something that will not be noticable enough to benefit you. A shaft will have many spines in it. The idea is that the primary spine will be found and adjusted to the clubhead so that there will be a minimum downward flexing of the shaft and return the clubhead to the ball more consistently. However the clubhead will twist on the downswing which negates the supposed benefit of spine adjusting. It is doubtful that even a pro would be able to tell the difference.