I used to pull 7k trailers without anything, passing me trucks would cause some sway and I'd have some at other times as well but I didn't think it was too bad. Then I bought an Anderson hitch with both WD and sway control and the difference was night and day. The big moment was catching outflow gusts from a thunderstorm resulting in a 70mph crosswind. I had to slow down as it was wanting to push me off the road but the trailer stayed straight behind me.
Now I won't tow without it.
Just my 2 cents.