They work pretty well with cylinders that have a little wear in the notches in my experience.
Also, they "tighten" up the whole action for me. I have one in my old Model 10-5. The entire action is a little tighter if you get what I mean. I like how it made the action feel with a slightly reduced power rebound spring and mainspring.
(That combination of springs felt the best to me after trial and error. Plus, the cylinder stop, with the heavier spring, works better in this old, fairly heavily used gun.)
Just a personal preference on my "mixing-up" of the springs for me, but I think the main purpose is to make the cylinder stop "grab" the notches better in cylinders that have a little wear in the notches. (Maybe a gunsmith can weigh in on this?)
Edit: Alot of guys buy an oversized cylinder stop or just buy a new cylinder stop to solve wear problems on the cylinder and/or wear on the old cylinder stop. (Cylinder stops can get worn down also from my experience.)