I think you're not supposed to use it as food because it is mostly corn, which is mostly starch and sugar. Young chickens especially need to have a particular nutritional balance, notably protein, which is not supplied by the scratch.
I've read that it's used especially in the winter in cold areas because the corn = calories = warmth.
That said, I give a handful to my 16-week-old chickens as an enticement to come into the coop at night. They love it
It does not have enough nutritional value. I never use it but when asked about it I always say give it in small quantities as a treat only and only give it in early morning or late evening because it can raise the body temp of the birds. The birds love the stuff but it is the equivalent of handing out jolly ranchers to everyone.
I just bought 65 bags of layer and only 8 bags of scratch. It is just a treat, gets them in the coop, or gets them out from under my feet when working around them or lets me show off ALL my free rangers when company comes. Its like a horror movie with all these birds of many ages and breeds come running to one spot to get that treat.