There are 3 schools of thought regarding internal parasites:
1. A flock with strong immunity will have minimal parasite load. Any birds with a larger load are weaker flock members, and should be culled. Parasites are not an abnormal finding, and a minimal load is acceptable. A free range flock will self medicate with the many plants and herbs that are available. The flockster who has this natural approach will often plant some herbs that are known to be natural helminthicides. An other natural apporach is the use of mild soaps like Basic H. Many old time farmers use this with all of their livestock. The beauty of soap to kill worms is that it kills them by breaking down their waxy skin, and they are not able to grow immune to it.
2. Don't treat unless you see visible worms. Or, unless a fecal float test indicates a worm load severe enough to warrant treatment.
3. Treat several times a year with a specific treatment plan which may include alternating medications.
As you figure, I'm of the #1 school of thought. My flock has never been wormed, nor have I seen any signs of worms. Bee Kissed keeps a natural flock as well. When she processes birds every year, she does an autopsy inspection, and does not find any worms.