A lot of members don't use them and don't have any trouble pulling their pups without sway as long as their pups are loaded correctly. We have a heavy Niagara and we started using one after our first camping trip. We didn't have any trouble but did have some sway. Since using the sway bar we have noticed a big difference and we would not go without one now.
I've had two trailers, both at around the 2000 pound mark loaded. I have never felt the need for a sway bar. Never had a problem, so I don't see the point. Maybe I would if I ever tried one, but so far, no need