Have them. Use them. You have to keep them clean and free of debris just as any other item coming in contact with the gelcoat or paint. I wash the boat regularly, so they get rinsed and cleaned in the process. They reduce the abrasion of the hull surfaces. Other methods to accomplish this already mentioned probably work just as well.
Wifey B: I think covers clean up easier than fenders and while they're not cheap, cheaper to replace than fenders.
I don't find docking does so much to them. It's locks that just tear them up. We use fender boards where we can in locks, sort of sacrificial. We did more covers in, and a couple of fenders, on the loop than all the rest of our cruising combined.