This add-on is absurdly useful for Enterprise IT administrators. It enables easy use of dedicated admin identities into separate containers for isolation form normal productivity work, and is particularly useful in contexts like Microsoft 365 / Azure where logging in to the same URLs multiple times in the same browser needs to happen with separate identities that have separate permissions granted.

Multi-Account Containers is a game changer for how I interact with a web browser. It's one of those pieces of technology that once you use it the first time, you simply can't go back to the older means of interaction absent the new features ever again. The degree of quality of life improvement I've received in using this add-on is gigantic, probably the most impactful change since discovering tabbed browsing in the late 1990s.