It lessens the cognitive load in easy driving situations, such as sitting in a queue on the highway. A hand on the wheel, your foot wherever you want, eyes on the road is enough. Just knowing that the car will take care of the small things is a massive offload.

Also, you learn what your car is good at and bad at, and plan accordingly. I know my car is bad at handling drivers changing into my lane too close to me, so I take over in those situations.