Polishing can make some scratches less noticeable but not make them disappear entirely. Buffing it definitely thins the metal, but not significantly. You wouldn't notice it. Then again, you shouldn't be buffing it every month or so cause then you'd see it!
If it really bothers you, you could have it serviced by Rolex. They have to be serviced every 5 years or so anyway, so you shouldn't worry

I should mention that when there were some very minor scratches on my Rolex, hubby buffed them out himself with a 3M sponge!

If you're brave enough to do it yourself, you should go to timezone.com and do research there. They have a lot of info and recommendations on cleaning/buffing your own watches. HTH!