I used to be a tree-style-tabs power user but at some point I went back to regular tabs. I find that the amount of horizontal tab space is pretty close to the actual number of things I can usefully have open at once. Seeing the tabs get "squished" is my reminder to close the ones I no longer need. I was using the tab-state as a sort of short-term working memory and I don't think it was doing me any favours, particula…
I actively use tree style tabs, and have dozens to hundreds. With auto tab discard, it's not taxing. This is because I basically use tabs as bookmarks relevant to a project or subject area. Bookmarks are also tree-structured, but are much more high-ceremony to create. To my mind, tabs and bookmarks should meld into one. If you don't close a tab actively, it stays deactivated, its tree likely gets collapsed until need…
Different people have different needs, so it is useful to distinguish between the two. For example: I have groups of bookmarks that I like to open as tabs in a separate window. If I only need them once a week, I want to close the window when I am done and pull them up again when they are needed. Fishing them out of a history of all of my browsing is something that I don't want to endure (even if they are stored in the history as a group).
Other people have other needs. Some only want an extremely limited number of tabs open at one time (presumably to help them focus).