The main reason for the adjustable wheel track on ag tractors is for cultivation, spraying and similar row-crop operations where you want to center the tires to minimize crop damage (this does not come into play with any of the operations listed above). Besides that, a wider width will obviously increase stability but will limit places where the tractor can go (between trees, barn doors, on trailers, thru gates, etc.). I generally prefer the narrowest width that will give me adequate stability. Since there are not any hills on my place, I usually go close to the narrowest setting. The exception being tricycle tractors which are inherently much less stable (and no longer made for this reason), so I move the rears on those out to the wider positions.