It will be about 13 months before I have to make a decision about that surgery. But the big advantages I see are being able to wear a bikini in public without having to either wear a very tight gaffe underneath or do a tape and tuck, or wear a suit that is a)thick fabric, b) wide in the crotch and c) has a printed pattern (hides the stuff better than solid colors).
Then there is being able to get naked in the gym locker room while changing for the pool.
Aside from that I see no real advantages, and my wife would very much prefer that I keep things the way they are down there.
I have an MTF friend who is an MD and she has elected not to have the surgery. She had extensive FFS, but not below. When I asked her why, she said, "They train us never to do unnecessary surgery." She went on to say that she needed FFS to pass, but she had no bottom dysphoria, and could tuck it into a bikini, so she considered it unnecessary.
So, just another point of view to consider...but if you need it in order to function sexually, then it is medically necessary. I just wanted to put things into perspective.