Ah, so you’re saying having old containers is useful in case something breaks and you need to roll back? In that case would it be just the immediately previous container, or would there ever be a need for a container from wayyyy back?
I know the macOS comparison isn’t perfect but my point is I’d never ~ go back~ to a very old OS, even if certain legacy apps only run on the latest. If someone gives me a concrete example of “here’s a case where I actually did end up needing one of my old Discourse containers from two years ago” I will go ahead and shut up 
This is just something I’ve wondered about for a very long time tbh.