I can't see any good argument against adjustable-shafted drivers. If you are like my friend Bill, who can pull a drive 80 yards left on one hole, and then slice it 80 yards right on the next one, then maybe. 🙂 But if you have a consistent swing, being able to fine tune the ball flight is marvelous!
I'm sure there are some who constantly move theirs around, but I haven't observed that. I rarely move mine, once I get it dialed in.