I combine containers with running multiple copies of Firefox under different profiles. I've been using multiple profiles for years, and I think it still offers some advantages even with container support. The big one is that one instance of the browser can crash or be restarted without any impact to the others. It also distributes resource consumption over multiple independent processes, though I'm sure there's some overhead in this approach. Finally, it allows slightly different settings for each profile depending on need. I manage common settings with a user.js file.
One profile is for logging into various services I regularly use, one is dedicated to day-to-day surfing, one is for local development (there are no addons in this one), one is specifically for webmail, and one is specifically for Trello. Containers are most useful with the first two profiles...especially the first, so that the various services have some level of isolation.
I have a container for each of my prod AWS Accounts. I do a lot of infra work, so being able to compare different accounts, and have them all signed in at once is nice.
Or if you're a consultant working on mobile apps for different clients, having separate containers for each client allows you to be in all of the client's Google Play Console at the same time in one browser.
(Or in multiple accounts/logins of Twitter, Facebook, Gmail, Outlook, etc...)
Pretty much those, plus WhatsApp (distinct from Facebook), because I don't use Facebook, except as being tracked across the Web, but I'm using WhatsApp Desktop extensively, and wanted that separated.
I might add separate containers for separate Twitter accounts, because the multiple account UI on Twitter's web site is atrocious, IMO. I'm constantly "in the wrong account".
At work I set up a container for all the domains and servers my company uses versus everything else.
I have containers for: Banking, Google (and the few places where I use Google as my SSO provider), Work, and then a general "I'm Signed In" container.
I also use the Temporary Containers extension for added privacy, though it's... still pretty rough around the edges, particularly when dealing with sites that use SSO (since kicking out to an OAuth provider causes a new temporary container to be opened, which then messes up the auth flow).
I have it similarly, except that I have Google work and Google private separated.
Unfortunately at work we are using a lot of OAuth, so I am supposed to use AWS and others with Google authentication. Which means that I cannot isolate them anymore. At the moment I still use my old AWS IAM account, but the plan is to remove the credentials. On other services I have never had any separate credentials :(
Personal, Banking, Work Place 1, Work Place 2, Junk (for social media) and then a couple others as spares
My key use of this is to manage multiple login sessions to the same site. Having a bunch of spare containers lets me do this in the same browser window. And I don't have to worry about closing them (compared to using private browsing)
