One situation where light is actually "wasted" is the video aspect ratio of 16:9 on a full frame sensor. Canon should allow us to use the whole sensor for video if we really want. Not everybody makes videos just for 16:9 displays. Canon gives us the green area for video, while it could give us the red area or (if 16:9 is needed) the blue area. The green area does not reach the image circle with any of its corners. So video is always cropped.