Minecraft wiki entry for Hunger_management, associated text: Advantages:
Restores 7.2 saturation.
Chickens are easier to find[verify] than most other passive mobs, and also lay eggs and provide feathers.
Chickens can be bred with any of several kinds of seeds to breed, and the eggs make even those optional.
Only a single chicken is needed to start a chicken farm; the eggs can be collected until more chickens spawn (which can then be bred as usual).
Again thanks to the eggs, cooked chicken can be farmed completely automatically, compared to farming of other animals which needs the player to breed the animals.