I’m curious as to what function coxcombs and wattles serve. I mean, I know that those of domestic birds are commonly cooked and eaten in French and Italian cuisine, but I’m more interested in what use they are to the animal before it’s slaughtered. Are they some sort of sexual characteristic with a role in sexual selection? Heat dissipation devices? Or just the product of some random mutation that hasn’t been selected against because it’s neither particularly useful nor problematic? An awful lot of birds in different orders seem to have one or both of them: chickens, turkeys, and pheasants; wattlebirds; some vultures; cassowaries; and some lapwings. It makes me wonder if the coxcombs and wattles originate from some common ancestor (in which case, why did so many species in the aforementioned groups lose them?), or if they evolved independently in several species.
Nobody wants to answer? What’s the matter? Y’all chicken? 
You may call me a turkey, but this is what I know about turkeys.
They are a sexual display. Tom turkeys have erectile tissue which makes up the waddle, and the long bit above the beak. When they are in full strut, wings on the ground, gobbling to call in the hens from the next county, the long bit above the beak can fall several inches below it. Later in the year, after breeding season, they are greatly reduced (usually <1")
I’d assume that chickens are similar, in that the cocks are sexual display organs. Every hen likes a big cock. 
The enlarged and brightly colored folds of skin on some birds serve largely the same function that the enlarged mammary glands of human females. They are a sexual display. Some birds have fancy tails, some have fancy feathers, some have fancy skin flaps, some have fancy dances, some have fancy nests, and the point of all this fanciness is that the fancier you are the more the chicks fancy you. Fancy lads mate more often and pass on their fanciness to their offspring. And the females evolve to appreciate fanciness, until you have incredible sexual displays like the peacock’s tail. The rooster’s comb and tailfeathers are the same thing. They turn on the ladies.