There is a big difference between doing the absolute best for the animal and doing the best for a business or to make profit. Chickens do best free feeding. Is that the most cost effective? No. They will waste a little feed but they will not harm themselves doing it. You can harm them trying...
Chickens will not overeat. Nearly everyone on here free feeds and their chickens do not over eat. Mine free range, have food 24/7, and during most of the summer don't even eat it at all. If you only give something in limited amounts though they will eat all they can even if it's an inedible...