Flex, one of the theories behind why package bees requeen themselves is that they are absent brood smell for a long enough period they think something's wrong with the queen.
Those are queen cells. Now imagine this scenario, These cells are coming right off the bottom of the frame instead of where they are at. You have two supers, the QCs are located on the bottom of the frames of the top super. You don't know it's queen less. You remove the top super and place it on something solid like a table top or hive body top. Now all your QCs are damaged beyond repair.
That's why it's a good practice to either place the super on an empty super or when removing it - lift it up from the back, slide the front edge (making sure only the edge of the front face of the super is touching the super below it) toward you a few inches and look under the frames.
yep, I done it - but I got away with it because of the QCs in the middle of the frame.