Oh for lost technologies! I have seen builders placing transoms in homes to help create a dramatic look, but not really for their intended purpose. I am surprised to find that many people have forgotten about transoms though, considering that they may be great for green and energy efficient building practices.
You have probably seen a transom in an old film, if not in person. The idea is to let light from one room pass through to another room or hallway by having a window above a door. Some builders use large windows like this to help with the feeling of spaciousness while keeping rooms separate. By having a transom above a bedroom door, you can help light an interior hallway, saving energy by not using the light. However a transom can (and did) do more. If it can be opened, you allow air to pass from room to room, even when doors are closed. We feel comfortable in our home when the air moves freely about, not with a lower temperature. By lowering the temperature, you cause you air conditioning system to come on and move the air through its fans.
Transoms can be quite decorative. I remember one from Japan, that had a wood carving of a cliff side. I have seen others with stained glass. So consider a transom when thinking of building green.