It would increase the section width, but most classs racers put 9" slicks on 10" rims when possible. It allows more airpressure while still maintaining a good "footprint" and helps the sidewalls live longer due to less wrinkling. Just like any other combo, gotta test to see what pressure works best for you.
I have Hoosier lightweight 9" radial slicks on 10" Holeshot wheels.