but I don’t know any use-cases for it. Having separate PC for each user is fine, PC are cheap nowadays. Can someone tell real world use cases of multiuser GUI sessions?
Please don’t think that with a “rich 1st world country mindset”. One PC per person may not be affordable at all for some people with economic hardships. There are families in other countries in the world that barely have one computer for all the family. There, you would like to have one account for the mother and another for the father for things of their jobs, and another one(s) for their son(s) or daughter(s) to do homework. THere you have a use case.
Here’s another: you want to use another separate account for high privilege tasks, while leaving your main one you use daily as an unprivileged user for security and privacy reasons, specially with the dangers of the web. Or for maintenance reasons.
Also you would want to have more than one (unprivileged) account (besides the privileged one) in case you want to completely isolate files and mails of one account from another for whatever reason (you don’t want to mix things up…).
Or your company that uses Haiku wants to use the same computer with Joe in morning shift and Mary in afternoon shift.