You would be amazed how many transitioners come to a conclusion that transition isn't the right thing for them, after a year or two or four living "full-time" and being on hormones. What seems like an overwhelming change and each small step brings a new excitement, often turns into reality, which is living a life as an unpassable trans woman. This isn't a situation for everybody. And not everybody has a chance to afford a full-FFS, which could cost from $20-30,000 with reputable surgeon... and even that alone might not be enough. Too many realize a few years later that they need to be really passable, not just somewhat passable, in order to find a decent job, and to be able to find a life partner, and to be able to be happy. And because hormones and attitude can only do so much, and they don't have a money for expensive surgeries, many realize how much easier it was before. Waiting with SRS until you lived at least for few years (not just one for old wpath' sake) "full-time" is a smart thing. Better be late than sorry.