Its all personal preference. I personally like sway bars on sleds, trail and off trail. I like it on my 42" wide off trail sled, and like it on my 37" wide off trail sled. Though I don't ride the 42" wide sled much, its just a backup that the engine is out currently.
Some guys like them, some don't. Try it and see what you like. I don't off trail ride in the midwest either, so maybe its different here?