Yes, you do. The sentiment here in California is that there are a significant number of people who go shopping for long periods, or even go as far as to leave their car overnight. They couldn't care less about a notification. The truth is, for all of us who arrive and leave a SC and see a car that was already there and still there when we are done, we have no idea if they parked there for hours, or arrived 1 minute earlier with a lower state of charge.
So far, with all the discussions about notifications, leaving notes, throttling charge, banning use, and everything else under the sun, the absolute BEST suggestion I have heard so far is dandelot's idea of having a light on each stall. It is frickin' brilliant. It would take a real narcissist to leave a car at a busy SC after it is full if they know that this is being advertised to the world. I would take it a step further: Green when charging, Yellow when nearly full, Red when complete.