Trying to maintain a steady speed and conserve gas is a fun challenge, but a bit pointless, because a) it's a distraction from more important tasks, and b) the computer can usually do it better than I can.
I did a 6 hours trip with a friend continuously putting his foot up and down on the throttle, and it was the most gruelling car trip I've had I think.
When I asked he said it was "to keep control on the car". I'm a patient friend.
Not entirely true. I've been to German driving school and my father really pushed the concept of smooth throttle control on me as a beginning driver. Be smooth always. However, as I was able to afford higher and higher performance vehicles my take on the smooth maintaining of speed without noticeable accelerator input has changed. While I'll drive my SUV very smoothly, when I drive my manual six speed German roadster, my style is entirely different. Because of the weight, size, and HP, it's really not possible to drive it smoothly outside of tossing it into 6th which isn't terribly "fun". In the gears where it's "fun", it's a very much "on" or "off" throttle experience simply because of the HP produced by the engine.
a) you don't want to drive them smoothing because that's no fun - even for just the exhaust note & b) It's actually difficult to drive them smoothly because of the torque/HP.
It doesn't mean you are a bad driver, it simply means you've adjusted your driving style to match the car you are driving.
In her defense, she learned to drive in a very different environment (dense Chicago surface street traffic).
Anti-lock brakes were the first such system. Before, you had to pump the brakes in an emergency, a practice that was difficult to execute even without the shock of an impeding accident. That system alone certainly saves thousands of lives every year.
That being said, it's always been while stopping for a light, not in a case when I had to swerve, so its never prevented a crash for me, but it really is comforting to have it.
The star usecase is to set cruise to be very near the speed limit, such that after acceleration events like overtaking, you coast back to highway speed.
It's a low-effort way of ensuring that one will be compliant with speed laws most of the time, yet maintaining a steady pace. I too prefer to be 'actively engaged' while driving, but in my opinion the reduction of constant acceleration input is a welcome convenience.
'Adaptive' cruise control, on the other hand, feels to me like riding on a tenuous rollercoaster. It's intended to let cruise control be usable in packed traffic, but it requires one to cede a lot of trust and control to the machine in ways that physically make me uneasy -- and it doesn't help that the exact behavior differs between models and manufacturers, so that trust doesn't automatically transplant into a different car.
Part of the problem is, again, with terminology. Ever since Adaptive Cruise Control proliferated as a term, it drew a parallel to classic 'Cruise Control', which I think is a mistake. Classic Cruise Control is a fire-and-forget, non-safety feature that's simple to reason about: do I want the car to gun it at a constant 70 mph, or no? You can run a quick mental judgement call and decide whether to engage it or leave it off.
'Adaptive' cruise control fundamentally about maintaining following distance, i.e. tailgating restriction. It's a safety feature. It's a button to "proceed forward not exceeding target speed", but if it gets disengaged for any reason then you can easily overrun into the car ahead. It's a safety feature with the UI/UX of a non-safety feature, so it's always opt-in (!) -- which is simply horrific.
All safety features in vehicles should be either always-on, or opt-out, and NEVER opt-in. On a modern car, tailgate restriction should be on by default, with a button unlocking the car into free-throttle mode. Braking -- alone -- should never disable a safety feature.
On ceding trust - at least with the ICC system in Nissans, it's A) far back, which gives more reaction time B) quite easy to tell when it sees the car in front vs when it doesn't. You're ceding trust, sure, but you can also verify easily.
Your 'tailgate restriction' bit is effectively a more agressive form of collision warning/forward emergency braking, and FCW+FEB as far as I know is available on all or at least most vehicles with ACC/ICC. Unfortunately, the realities of city driving means that 'maintaining distance' is a goal in some cases (i.e. just got cut off, tight merges, etc) rather than an absolute directive - frankly, something trying to force me to a certain distance away from the car in front of me would be more aggravating than useful.
Are there cars that have ACC and don't have AEB (Automatic Emergency Braking)?