Some people do regularly worm, but others won't unless they know that their birds are carrying a worm load. There is the worry that the parasites will start to build resistance to wormers so they should only be used when necessary. You can get a fecal float done at the vets to reveal whether there is a problem or not.
Some flocks will have more problems than others; there's no one answer for everyone. Having fecals run at the veterinarian's is the only reliable way to ID intestinal parasites, and if found, especially in large numbers, worming can be indicated.
No one product kills every parasite, so knowing what's there is necessary to be effective.