1. if your talking about the main setup screen, and the repair install, then your files (pictures, documents), should not be affected. Because it's just like installing on top of your old system files. That's why it's called repair install.
2. if you are talking about pressing R before the main setup screen loads, that's only for someone who wants to fix something the old fashion way, using command lines. It has nothing to do with actual reinstalling.
I'm guessing the first case. But if you want, you can write us the actual problem to see if U need a repair install.