Earlier quoted context omitted.
I think the point with those supermarket cameras is to influence behaviour, not to surveil, I doubt they are even recording. When I was a kid (maybe in a worse area than you) there were CRT TVs by entrances of supermarkets showing a live feed of you walking in. People behave differently when they feel they are being watched, it's why they have creepy CCTV posters with big eyes on them. Probably the same reason for ev…
Yes, this has been under consideration when thinking just how much raw footage would have to be stored for 4 or more self-checkout cameras for every shop. Probably multiple terabytes per day, per chain, just for London. There is also the classic 'plastic camera with blinking LED' CCTV installation, intended to deter theft in a more lo-fi manner. As an aside, the artist John Baldessari made an installation in the Tate…
Here's a good reference point: if you have one hard drive per camera, and record at 1Mbps, you can store 5 years of footage.