Obviously the benifit will vary a lot person to person.

Part of over controlling is just moving the sticks too far. But part of it is getting the connections between the eyeballs, fingers, and brain wired together so you know that what your fingers did should look like at the other end. I'm doing a lousy job explaining it. Some people get it naturally, but some don't. Some people naturally "feel" the cause-effect and the time delays and how the plane reacts to the sticks. Some people don't. If you don't, then a park flyer will help with this kind of thing, and will, in fact, help with over controlling.

I guess you could say that it's not so much over controlling as not-quite-controlling, knowing how to start a roll or turn, but not quite knowing how to stop it. This isn't quite the same thing as moving the sticks too far. That might be a better way of explaining it. YMMV.