On a long highway run I find cruise control helps with economy more than anything else. This is because it stops you unconsciously accelerating when you don't n

On a long highway run I find cruise control helps with economy more than anything else. This is because it stops you unconsciously accelerating when you don't need to. It also gives you the chance to wriggle your feet and legs a bit which can be nice. It's only really of use in light traffic as it'll quickly put you in conflict with other drivers who aren't using it. The other benefit is cognitive, but not in the way you might expect: it's not relaxing to turn it on, you still have to steer and very much drive the car; it's more that when you get bored, you can turn it off and "hand fly" the car again, and that change of modality is refreshing in itself. (This is purely an aside but I have a temporary soapbox so why not. I'm skeptical of more advanced forms of cruise control, even simple things like adaptive. Anything that reduces your need to concentrate tends to leave you open to daydreaming (never mind actual distractions like phones); an example of the "TSA agent problem" where staring at a screen of benign bags all day turns out to be a bad way to detect guns in hand luggage. Better I think to have nothing, absent sci-fi-years-in-the-future autonomous cars where you can sleep while they're underway. Humans are awful at passively waiting for something out of the ordinary to occur; computers are great at that. Computers suck at common sense and detecting intention; humans are amazing. The current state of self driving cars plays to both actors' worst weaknesses!)