I use lanekeeping on the freeway, usually with adaptive cruise control as well (subaru). I focus more on the Big Picture of all the cars around me, can see further and have a better sense of who is doing what. That's anecdotal, of course, and could well be placebo effect, but I still pay a lot of attention to the road.

Plus, lanekeeping can be really annoying if you rely on it all the time. The car sometimes tends to drift back and forth in a lane a little between corrections, instead of just going straight. So: you're still steering. It's just that you're steering less and have a defense in depth against loss of focus, and can drive without exhausting yourself.