well, i can think of at least 1: if you use 5mm spacers you effectively increase the track of a 225 tire to that of a 235 tire. you still have only a 225 tire, it just has a wider track, which increases lateral stability. spacers must be hub-centric, of course, for our vehicles....
Reducing the offset, while keeping the others the same will move the tire outward. But apart from looks I don't see the point in doing that.
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