Its not just candy, its supplement food for chickens as well. In my country it contains all kind of grains, seeds and pieces of corn.Scratch is chicken candy, a mix of seeds and other tasty tidbits.
Normal chickens (not the factory hybrids) that truly free range in a field with plenty of food just need what they find and its common practice to give them a few handfuls of scratch in the evening so they can roost with a full crop.
It’s true scratch is a treat for chickens that are locked up. If you have a heavy breed that is not active, the chickens get too fat if you give much scratch.