Commercial feed is, generally speaking, a balanced diet for chickens. There are different formulations available for different applications. Higher protein is good for meat birds and winter, and for growing chicks. Some breeds do better with different % of protein, etc.
Scratch feed isn't always for a "treat". Chickens get bored. A handful of scratch spread in their chicken run/yard will keep them busy all day. They also get nutritional value from the scratch feed.
We currently have 18 chickens, 17 hens and one rooster that we are wintering. Every morning, they get about 2-3 cups of scratch grains that are tossed out into the chicken yard. Right now the scratch grains we give our chickens is a mix of mostly oats and whole wheat, with a little cracked corn. They prefer the whole wheat right now. They have "all flock" commercial feed available at will all day long. They also have oyster shell free choice all day long. If they want the oyster shell they eat it. They usually fill up on commercial feed, take a few pecks at the oyster shell, and range around all day eating seeds, bugs, dirt, whatever. The chickens will eat what they need. Mine don't overeat either. Healthy, physically fit chickens that each (not the rooster of course) lay an egg nearly every day or so.
