The downside is that offsetting the wheels puts more stress on the axle bearings.
The upside is that at only 1" of offset, it won't increase stress much.
The downside is, at only 2" of total offset, you probably won't be able to tell any difference between the two sets of wheels.
Check that the increased width doesn't make the tires wider than the deck.
When mowing sideways on a slope, keep your tires aired up and engine oil topped off. Make sure you aren't exceeding Scag's recommendation for max slopes.