I let my babies fly until I can't stand it anymore, but I have a high tolerance for inconvenience. When done properly, a bird will be able to fly a short distance, control his flight and be able to make a safe landing. When a bird's wings are clipped incorrectly after he learns to fly, he may lose his confidence and the capability of controlling his body. He discovers, through pain and even injury, that what he previously learned about flying is no longer possible. The primary flight feathers are the only feathers which should be clipped.
Many people clip birds' flight feathers at, or slightly below, the level of the upperwing coverts.
With this method, the birds will be after the exposed ends of the shafts all the time and the shafts will become splintered from the constant grooming. The sharp, splintered ends seem to irritate their body and bother them psychologically. They are never satisfied with the ends of the shaft. They can't groom the cut shortened feather into submission and order. There is a physiological component as well as a psychological component when one considers how important flight feathers are to a bird's safety and life.