In the bedrooms because often the glass door bookcase we find gaps do not know what to do with them, I say cupboard that is usually the main cause, but there may be a gap for any other structural motif of the room. These holes provide us with a storage space do not say extra for it is a piece that was already but almost extra storage for such a bookcase, cabinet, desk, improvised cobbler.
Another frequent places that we find where we have a gap, is on the wall of the headboard, most often due to heating i.e. radiators, they are set into the wall and go right on main wall which is supposed to go the headboard. As with simple glass door bookcase, you can take advantage of that gap by giving a purpose which otherwise could not be done. Of course, make sure to place everything is secure and safe is not going to be that one night we wake up with a bump on the head. These are just some ideas and examples of how to leverage glass door bookcase with holes in a bedroom if you search the net you will find many more examples and ideas.