It's specifically an addon for folks who normally have dozens (or hundreds) of tabs open, and I can only imagine it's actively detrimental to someone who only has a handful of tabs at a time.
IMO you should just be thankful that your workflow/habits haven't develop in such a way that you benefit from the organizational power of tree style tabs ;-P
I'm a zillion tab person. But even aside from that, it improves the usability of the browser.
A problem with browser UI is that - given our monitor form factor - it makes text hard to read. Studies show that very wide columns of text are harder to read than something relatively narrower.
By changing the viewing pane of the browser, moving the tabs off the top and to the side, we mitigate that extra-wide shape somewhat, making the text more easily readable while giving ourselves a bit more vertical space.
IMO you should just be thankful that your workflow/habits haven't develop in such a way that you benefit from the organizational power of tree style tabs ;-P