I have around 18 birds in total, mostly hens but a rooster and a duck or two. They free range over several acres of pasture, get grit from the driveway, etc. The only time I've seen them not want to come in and eat the feed I buy is when I have cattle in the pasture. Not only do they pick up what the calves drop when they feed but they peck through the manure and get more. Even then, they come when they see me to get their layer feed. They just don't eat as much.
Now, there's obviously an argument for me allowing them to eat what the cattle eat: mainly cracked corn and other grains and obv the protein levels are very different, etc but that's a whole other discussion. I assume they eat what they want and make up the nutritional difference with bugs, worms, and the feed I give them. Im not the type that make pets out of my chickens. I enjoy the hobby but I'm not very hands on. I want them to be healthy and productive. I find that free ranging works, but I still have to buy feed. In the winter they are cooped up with access to a run and feed costs go up. Ive found that if I don't do this they start nesting and roosting in different barns and areas I don't want them. If this wasn't a hobby it would make no financial sense at all.