I think what it means is that they only need breeders pellets if producing eggs that are destined to be hatched out. This is because breeders pellets have a higher level of vitamins and minerals in than layers pellets do. The higher specification is needed in order for the eggs to hatch out into healthy chicks, but is unnecessary if the eggs are only due to be eaten. A typical result of feeding layers pellets to breeding stock is when the chicks hatch out with bandy legs due to riboflavin deficiency. You also can get reduced hatching. However layers pellets are cheaper than breeders, which is why they are not needed if you are not actually hatching eggs.