Reflections are often captured, intentionally or not, in photographs, adding a new perspective within a photo that the viewer would otherwise be unable to see. Water often captures startlingly sharp reflections, like in the picture below. Sunglasses also add another scene within the photograph.
Montreux, Switzerland. The buildings and the two men behind the pool of water are captured in the reflection.
Santorini, Greece. My brother's extremely reflective Ray Bans portray a person who is actually behind me, the photographer.
Rome, Italy. Taken on my traditional film camera, another part of the Vatican, as well as the sun, is reflected in her aviators.