I would agree with OldHen but...This year for the first time I've dewormed. This came about because my close neighbor acquired a number of new chickens, one of which had worms and died (might have been compromised by other issues as well). Here's the Backyard reality, our flocks sometimes mix and who knows what came in on the new chicks? I recently lost nearly all my laying hens to a predator, so I didn't want to risk losing any of my new pullets or one older hen. We both dewormed in September, and we both just finished our second treatment with Valbazen, (1 cc for standard foul, 1/2cc for bantams/small chickens). We administered 2 doses, 10 days apart and eggs need to be discarded for 10 days (no layers for me right now so it's not a problem.)
I will point out that non-worming advocates have a good point as far as natural order. I am not a production breeder or egg producer, I keep these animals for my own use and fancy. The loss of just one animal has a lot of impact.