Fender rolling is designed to take the rough lip of the fender and curve it back upon itself, it can also be used to slightly massage the fender out for more clearance.  When the suspension system and/or wheels/tires get beyond the original specifications that came on the vehicle, you run the potential into "rubbing".  Simply put this can result from stretching the limits of space provided or downright having the wrong setup.  The good news is with fender rolling this can normally accommodate both issues and worst case scenario is, it's always better than it was.