Barding

Does it do anything functional. or is it purely cosmetic?

I would like to know this too. I have all 3 type purchasable from the GC but havent notice any real difference when they are applied.

They're just for looks. SE said that barding will never add stats because they don't want everyone's chocobo looking the same. Said to just choose the one you like best.

Of course, the could also add a vanity system for Chocobos which would allow for Barding stats, but I'd rather their resources we're spent on developing endgame content and player housing. ;)