I think that scratch is a relic of the times when farmers raised their own corn, and fed leftovers to their mostly free-range chickens. It is a high-carbohydrate, low-protein food that chickens will eat in preference to the rest of their feed. I am phasing out true scratch, and making my own mix, for a lot of the same reasons that Ridgerunner mentioned. I am using sunflower seeds, oats, wheat and peas to create a grain mix that they can dig around for. I think it is valuable to give them a chance to scratch around for their food, which is what they seem made to do (left, right, right, left, repeat!), but I don't see a lot of nutritional value in corn (just cheapness).