Aspera, if you requeen every colony once a year, how will you ever develop a strain that will be healthy and productive in your area? Almost any beekeeper who doesn't practice requeening by the calendar, can tell you of a colony that went on and on and on, year after year. Always among the best producers, and the best winterers. Those are the colonies we should be breeding from. Annual requeening would kill all these breeders before they could be discovered.
So, what colonies do get requeened. Colonies with chalkbrood do. Hopefully with a hygienic strain. Colonies with poor patterns do, and colonies that winter poorly too.
If you keep a yard sheet on your bees, you begin to notice patterns. You see that colonies perform similarly from year to year. So, you have a colony that comes through the winter so, so. I like to see at least 9 frames of brood at dandelion. This one has 4. But the pattern is good...we'll give her a chance. You come back to re-super the yard a few weeks later. Most colonies have a hundred pounds on, but the questionable one has only a super and a half. So yoe decide to re-queen it. You break the hive open to start the procedure, and find hatched queen cells. OK, the bees did the job for you. Cool! So....
Next season, the colony has 4 frames of brood at dandelion. But, it's a new queen last summer. Give her a chance, right? I bet she has 4 frames of brood next year, too.
Some colonies are easy to read, when they need re-queening. Some are more difficult. It's the ones like my little example that you should focus on.
What I'm trying to say is, keep good records. That's how you'll know which colonies to requeen.
By the way...any colony in my operation that isn't performing well by dandelion, gets nuked with an overwintered nuc. That gets the first round of requeening done early. Later in the summer, any colonies not performing get broken up into 4 frame nucs. What's left on each stand...old queen and field bees in a medium or two...get requeened with the last round of queens. These are overwintered as nucs.