In my personal experience with being on T (and not having top surgery yet) is that it can worsen your dysphoria. It just felt like testosterone is out of the way, now I want my top surgery but can't quite afford it yet. My body was changing, but my chest was staying the same, which really hurts. However I agree with what others say about the changes of testosterone that are needed to pass, unless you are one to not care so much about passing...surprisingly trans guys like that exist, I don't know how they do it! Another problem with starting T first is if you're having trouble binding. Like me personally, I may be small but they never bind to how I want them, so I got all these changes and chest that's not really matching. So I have to shave my face and wear pants so I don't have to shave my legs and look like some sort of naturalist woman. Honestly in my opinion, both ways got ups and downs. I don't personally know if there are benefits of doing T first for the surgery, except it does help you build muscle easier, and it's always better to have a more muscular chest for surgery, also I've seen pictures and it makes the chest look better than with no muscle gain.