I just checked and I currently have 450+ tabs open. I closed around 100 the other day. I work on a number of projects at the same time, so I'll often have a bunch of documentation open for one project and then switch to the next one without closing everything.
I also research a project and then wait a while before starting it. This helps me get a better perspective on the project. I'll often leave my research open in a tab group so that when I start the project I can very quickly review everything and get up to speed. Using bookmarks in this scenario doesn't really work because bookmarks don't save session state very well.