I have pulled trailers for close to 20 years, the biggest was my 30 Foot award. Sway control and WD is all about keeping you in control of your rig. Things can go badly very quickly with high winds, cross winds trailers passing, blow outs swerving and the lists goes on. The wd keeps the front wheels on the ground allowing you to steer you vehicle. The sway keeps you from jack knifing and fish tailing especially in winding , wet conditions. In my trailering career I have dealt with blow outs, swerving to miss animals and other vehicles and panic stops for various reasons including large rocks on the road way in the mountains., I one time came around a curve in the mountains only to find some people who decided to stop their vehicle on a narrow 2 lane to take pictures.
When properly set up you should only feel the trailers when you are going through dips in the road as the bars will give you a little kick when they take over. I would love to try the new sway control that are part of the round or torsion bars, they say they prevent the sway before it starts as the friction sway apparatus controls the sway after it begins.