Guess it depends on why you are re-installing as to whether you want to keep those old files or not. That's not your character data that is getting deleted, just the game's executables and data files. Your character data and such are nested in your My Documents/My Games folder (just as a precaution though, you may want to back those folders up..I do it occasionally just in case). If you are re-installing because you suspect the game's files are corrupted, then you'd want to delete them anyway.