The scratch I buy has corn,wheat,oats and barley in it.I add blackoil sunflower seeds to it as well.I give them a few handfulls a day.All year long.
I don't believe scratch is like "candy" and is bad for them.I know it shouldn't be used as their only source of feed.
I also don't believe it keeps them warm.Unless you consider the exercise they get by scratching for it.
I look at it as giving them whole grains with protein(boss).I think wheat gives you quality golden yolks(not yellow) and oats are one of the best things you could feed a chicken.
I know many(very many) will disagree with this,but this is my opinon. Will