I also rarely have many things open, but now I have a bunch, and it's very useful to have them in group (in Edge). I am working on three services at once, because we need a change that impacts all three, and they depend on each other as well. I have my ticket open, and its parent ticket as well for context. I have the pull request, the build pipeline, and the deployment settings open for each service. I have an AI open, an API reference open, and I have 1-2 random internet searches open. All in all, this is 14-15 tabs.

I can imagine that other people who have different contexts, and some web apps like mail, im and socials, that can easily make use of tab groups. Grouping and coloring them makes it really easy to not get lost in the bunch that is open at the same time.