And Turbo just answered my reasoning. If you've got flares, it's not that bad, but without flares, a good 2.5" of tire sticking out of the fender.
To probably understand better, I would learn about wheel specs and how backspacing is measured and offset, etc. There are some good websites showing how wheel specs make a difference. Google it. Say a 15x8 w/ 4" backspace wheel sits just inside of the fender flare. A 15x10 w/ 4" backspace wheel sits 2" past where the 8" w/ same backspace sat. With flares it ain't that bad, but without, they be stickin' out.
'01 XLT disguised as a '03 Fx4 Level II.