The therapy I have had wasn't related to being transgender, but I will say how much it helps of hinders totally depends on what you need. For a few sessions, the therapist wanted to try and help by trying to get me to be positive about my parents, which wasn't at all helpful. She realized this wasn't helping anything, and really had me work on trust issues on people not my parents and that was very helpful... I used to suffer some pretty bad social anxiety and basically after a few sessions with her, and looking at things in a different way I basically overcame it.
I could see however, if she had been stuck on her initial concept that I was the problem in my relationship with my parents and that is what was causing my issues with socializing and trusting, that we wouldn't have got anywhere. She didn't have some strong professional ego, but if she did I would have expected her to do exactly that. In the end, she realized that I was right more or less and my parents were not only the source of the problem in my relationship with them, but she supported my bid to seek emancipation from them. Which with the help of my brother stepping in for legal guardianship I managed to get at the age of 14.
So my point in that whole story is that, if you have the right sort of person I could see it helping dramatically as it did in my case. Honestly, GID, puberty, and a terrible life at home probably would have meant I wouldn't have made it out of my teenage years alive if not for at least a few adults like my therapist listening to me. I am very thankful the school set me up with her even if their reasons where shaky (I wore lots of black, and a pentagram necklace so they thought I was going to shoot the school up or something-I wasn't).