Lower numbers than these specs causes the tire to be farther from the center of the vehicle. This can not only cause rubbing on the upper fender well but also in the inside "splash guard" area, so rolling will not help all the problems.
Higher numbers will result in it being closer to the struts, which most often will cause rubbing on the spring perch and possibly the inner fender wheels on the front wheels.
Most often you will see wheels with oh so close offset, these are usually VW wheels remarketed for subaru owners who dont know any better.