These sites go into detail on feeding chickens. Probably a lot more information than you want, but I'll put it out here anyway.
Oregon State - Feeding Chickens
http://extension.oregonstate.edu/catalog/html/pnw/pnw477/#anchor1132074
Alabama - Feeding Chickens
http://www.aces.edu/pubs/docs/A/ANR-1317/
I'll go into recommendations. Different people obviously do things different than these recommendations and do fine. These are guidelines, not absolute laws of nature where your chickens are going to drop dead the instant you do something differently. They are meant to improve your odds of success, not guarantee success or failure.
You should regulate the feed of chicks differently depending on how you want the chicks to develop. For meat birds, whether Cornish crosses or dual purpose, you feed a higher protein feed at certain ages than you would future layers. At some stages of growth, it is the same. You want the meat birds to gain as fast as possible but the layers to have enough time to develop and mature so they can safely lay eggs when they do start, even if it delays the first egg a week or two. But as far as I know, you regulate this by the type of feed you offer, not by restricting how much they eat, except the Cornish crosses.
I have not raised Cornish crosses and have not studied their feeding. I know some people do sometimes restrict their feed, but I don't know the details of exactly why or how. I do occasionally allow my chicks or chickens to run out of feed so they will clean up all the old feed before it gets old and moldy, but this is when I can be around to monitor it. As soon as I see they have cleaned it up, they get new feed. I try to make feed available, 24/7.