I do not believe anyone at Microsoft actually uses it because if they did there's no way in hell that they would have let it be that bad.
It literally keeps every single conversation you've ever had in a big long list on the left, with absolutely no way to organize it, categorize it, order it, or in any way manage it other than deleting history, that's it you can delete history.
Microsoft's design philosophy in any of their products has gone from well organized menus to relying instead on a search bar. Copilot is a further addition to that design, with yet more pushes to never use a menu, but instead just tell it what you want and have it spit it back out. They want everything you make to go on OneDrive as well, so it can also be indexed this way. Teams works the same way. The big search bar at the top is unavoidable.
Windows search is complete garbage, which you might think is a counterpoint, but instead it's just that they only put work into having it serve results for cloud-indexed items or web results.
We used to use it before switching to Google Workspace (don't get me started on how much I hate that), and Teams wasn't too bad. But it had two things going for it then:
It was replacing Skype for Business which never should existed because it was so awful. Compared to SfB, literally anything was an improvement.
At the time, it was basically a Slack clone that didn't have everything and the kitchen sink bolted on yet and was decently lightweight if you used the browser version.
Maybe I'm remembering early/beta Teams with rose tinted spectacles, but at the very least the silver lining was that I no longer needed to keep a separate Windows machine running just for work IM.
I've had nothing but issues with it since their "upgrade" over the last year or so. It keeps cycling between the new and old versions when I open it, it often closes itself on my PC, and every time I try to pin it to my Taskbar it disappears.