Tires throw rocks. Fenders and flares stop the rocks. If your tires stick out past the fenders, those rocks go everywhere. If chipping your won paint and cracking other people's windshields is your thing, along with a vehicle that won't pass inspection in many states, then go for the wannabee monster truck look and have your tires sticking out past the flares.
Also, any offset past the factory spec increases the load on the wheel bearings. How much is too much? I don't know. I do drive about 80K miles a year locally in the land of giant tired everything and see wannabee Big Foots and Chevy Caprices with missing hub/wheel assemblies on the side of the road prolly once a month.