I typically have 50-200 browser tabs open, but I also usually have 5+ browser windows running. So, like, when I'm building something, I'll have the thing I'm building and all its parts spread across two windows, and a third window with all my reference materials. Then I can cleanly kill them all when I'm done.

I don't really know what I'd keep from those when that workflow is done. The thing is built, so I don't need any of it anymore.