That's a good question. Here in South Florida I don't have to worry about keeping chickens warm, so I just give them cracked corn for an occasional treat. The cracked corn is cheaper than the mixed scratch, which has corn & other grains & seeds mixed together. I use it for training purposes, to reward them for coming when I shake some scratch in a can.
With chicks I would give them just a little, for training or for a treat, I think they should eat mostly their chick starter to help them grow.