The old fashioned way to raise chickens was to let them forage for food out in the yard, supplemented with a little extra grain that is thrown out. So why do I spend $15 a bag on chicken pellets that I have to feed them every day? All of the current experts say that that is what you have to do to have a productive flock, but until I read this blog article by Robert Plamondon, I didn't know why: Why Chicken Feed?
In summary, yes, you can let hens fend for themselves if there is enough to forage, but they will likely be starving and won't be laying consistently. Supplementing foraging chickens with a balanced feed will yield high production with highly nutritious eggs and meat, much better than what is available from the standard supermarket fare.