I would never have a car without it (for motorway and long A roads, e.g. A1).
I find it extremely convenient, but the reason it’s a must for me is it’s safety feature. For example, if you are about to overtake a vehicle on a duel carriageway/motorway you will check your wing mirror and glance over your shoulder. If the car in front suddenly brakes, you will not see it, but your ACC will, stopping you.
I’m sure there is scenarios where ACC may be detrimental to safety, but think these will be far less frequent than the benefits it brings.