Like some of have said...it depends.
I towed my 3600LB hybrid with my Chevy Traverse for a couple years. I did not use a WDH with it because it was within the hitch and tow ratings, and I never felt I needed it. I towed at all speeds, in all sorts of conditions, and the trailer never even wiggled while towing. In that case a WDH would have been a waste of my $$.
My heavier (and longer)TT behind my (even higher rated) truck definitely rides and handles better with WDH. I towed a couple times without it, but have to admit the drive is more enjoyable with it.