Charging operators want good utilization. Some operators limit time when they have other motives than selling power. Generally, though, it is not usually in anybody's good interest to have people end a session early if nobody is waiting. That's why you want a way to say "I'm waiting" or "I'm on my way to the station."

However, stations like Volta which are there for advertising would prefer you vanish quickly, though they also charge at a slow rate.

Good point. The article about J1772 stations is of course for North America. Euro Type 2 and Tesla lock the plug in the car, not the plug. You physically can't unplug it without consent of the car owner. Which means nobody steals your station, but also means that unless you automatically unlock when full or at the time limit, you hog the station for no reason at that time.

Cars can and should be programmed to unlock when done -- but they don't want to do that with a mobile EVSE (like the one that comes with most cars) because that prevents theft. So cars need to know what is charging them. As the new digital protocol arises that will be easier.

J1772 is set up so that if somebody releases the mechanical lock, that stops the current, making it safe to then unplug. But it means you can't stop somebody from unplugging -- or stealing your mobile charger. I don't think mobile charger theft is a big issue today, but since they cost from $200 to $400, it could easily be.