The thinking is that a queen can only lay up about 9 frames completely (100%) and that brood hatches, opening up those cells for her to refill. I guess that would mean roughly 10 frames should be open for her to lay up, but then also consider that the bees need space for bee bread (pollen and nectar) close by to be able to feed that brood.
When I go through a hive I like to make sure that there is always space for the queen to lay and will remove frames of capped honey (deeps) during the summer and store them for safe keeping later. When I go around in the fall to see if hives are heavy, any that aren't get some of those frames dropped back in.