I’m not sure if it could be used to log into two different accounts on the same service unless you’re able to separate them by subdomain (like www.reddit.com vs old.reddit.com). I still find it very useful though. For example, I want to be logged into youtube.com but do not want my searches on google.com to accidentally be tied to my account, so they’re in separate containers.
(Browser fingerprinting is a thing and if I’m searching Google and watching YouTube at the same time, they can see I’m on the same VPN IP address. So it doesn’t guarantee anonymity, but that’s the trade-off you make for the convenience of using containers. When I want to make more private searches I’d use another browser, ideally the Tor Browser.)