Good that they are integrating that into the main browser.

For me the big use case is having different Google accounts active in one window. Work and private. And when I was doing freelance projects, I sometimes had 3 or 4 different Google accounts active. Plus assorted stuff tied to those accounts. Using different colors for each makes it easy to tell apart the tabs.

Another use case is if you are testing the same app for different customers with different credentials. I do this a lot and I have dedicated containers for each customer so I can easily switch with out having to log out and in a lot.

And of course some companies that can't be trusted with cookies, like Facebook, get isolated. I open that container less and less these days. But I still check every few months. I also keep my bank's website in its own container just on principle.