Okay, you don't have to have it. It's an important component of the deep litter method as it helps dry up the poo and keeps the flies down. Some people use it as a safe, effective way to worm your chicks should you feel the need. I wormed with it once before they reached laying age as a prophylatic, not because I saw any evidence of worms. Some people never worm, others only when they find evidence of worms.
DE is hard to find around here. I finally found it at the farmer's co-op, bought it one time and when I went back they had stopped selling the food grade kind. I musta raised a fuss (sweet lil ol' me), because last time I was in there the boy told me that had started getting the food grade kind again.
The other kind, the non-food grade kind, is used in swimming pools and has some gardening applications. It's easier to find around here, but you can't use it around your chickens.
From a previous post on another thread.
I agree with 'gritsar'. You don't really need it but It does help to absorb moisture and control flies and fleas. When the flies and fleas injest the DE is dehydrates them and kills them , "which is a fossilized deposit of microscopic shells created by one celled plants called Diatoms". Also the diatoms have sharp edges which are an irritant to the flies and fleas when they injust it. Recently we had a flea infestation. We had fleas everywhere except around the chickens. I sprinkle the DE all around the coop inside and out in their run and the spots where they like to dust bath. My husband bought the DE online but I'm not sure what site.