Anything where you have to log into an account with a secondary identity. So I have one for my work account Azure as it’s a different Microsoft account, one for work Google API projects as it’s a different Google account, etc. Used to have to use different browsers (even IE, ugh) but now there’s no need. I love containers (longtime Nightly user) but the UI is hard to get right and even harder to make intuitive, so I’m not surprised they made it an extension.