I have steering wheel knob in my car just because I think it gives me better control on the roads. There are no steering wheel knob laws where I live so I am completely within my rights to use one.
When I am using a steering wheel knob I know that the wheel will not slip through my hands. I have arthritis and my grip is not always very strong. When I am using a steering wheel knob I can steer using my entire hand instead of having to squeeze the wheel.