Capes are a form of Elvin status. Those in the Nobility wear capes. At Foxfire, prodigies wear short half capes to show that it is a noble school. While elves of the Nobility don't have to wear capes, even to formal occasions, it is highly recommended. In Book 1: Keeper of the Lost Cities, while bottling Everblaze, Sophie used her cape as a smoke filter.
Capes are often clasped with a family crest pin.