Chickens have worms. The objective is to keep the number of them down to an acceptable level. If they have worms really bad they will be skinny (you can feel the bones in their chest when you pick them up). The LA state vet recommends that you alternate ivermectin and safeguard so that you have less risk of the worms becoming immune to the dewormer. The Ivermectin deworms and kills mites and lice. A lot of people on here are hardwired against its use because it isn't "natural". Ivermectin is the main ingredient for heartworm meds for your pets and it is used to treat worms in humans, cows, pigs, etc.
DE does NOT deworm and Wazine is useless. I used both since I started keeping chickens. A few months ago, my chickens started getting "sick" and dying. I thought I was correctly deworming, so I called the state vet and they necropsied the deads hens. They said the chickens were full of parasites and that neither of the things I was using would kill the worms.