Are there any real life scenarios where an untrusted user is allowed access to a machine with an unprivileged account? I know there are (or were?) some public shared machines where you can ssh in for fun, but those aren't serious.

I'm thinking maybe a POS system or kiosk running Linux, and there's shell access? This could possibly also be useful for jailbreaking devices that ship with Linux, but are locked down... Maybe like a car infotainment system?