Line manageabiity -FC twists and flows off the reel when you don't want it to. Sensitivity. Casts further.
Disadvantages of braid: Sometimes it casts out a horrible snarl!
That being said, on my next DS outing, I'm taking two rods - one with braid/leader and one with FC. I will alternate casts and see if there is a significant difference in the bite. That will eliminate the skill of the other angler (or mojo) as a reason for more fish.