The biggest benefit I've seen in mixing it with my chickens' feed is that flies won't land in their poop. It really cuts down on the fly population. You can safely add about 2 to 3 percent DE (by weight) to their feed. I just eyeball it - maybe 2 tbsp. shaken into a large coffee can of feed.
The best part of mixing it in with their shavings is that the poop dries up to nearly indistinguishable. I use about one sifter-ful for each big bag of shavings. I do rake the shavings once a week to fluff it all up and keep it "airy." This really helps with the odor and my coop is always bone-dry.
I also had a really BAD ant infestation in my lawn - ant hills were on every square inch and killing my whole lawn. Wanted to let my hens out to eat them but too many neighborhood dogs. So I bought a gadget online called a Dustin Mizer, which spreads DE very, very thin (a pound of DE covers a whole acre!) and it got rid of the ants.
It also shines chrome like nobody's business . . .try a little on a damp rag on your kitchen or bathroom faucets, rinse, and be amazed!