I'm not sure but, I believe they may be necessary in certain set up's. Now, you are asking about Anti-Sway systems , Weight Distribution Systems are different. If you have a long, heavy, trailer then a Weight Distribution System may be necessary.
Like the OP I have towed trailers on the farm all my life and none of them had any system of any kind. I didn't even know such a thing existed until I joined this site. None of my friends use such a thing either. But, we all tow either short light trailer or stay close to home on back roads.
I tow a 20 foot trailer that weighs 4580 lbs loaded with a 2004 Chevy 1500 and it towes like a dream. I have no need for anything with this set up.
