Generally, the most important things an author wants to communicate to an audience are the things that are difficult to instantly demonstrate, such as a character's role in the story, personality, moral character, or whether the author wants the audience to sympathize with them. Note: while Hair Tropes are all tropes that have to do with hair, this is specifically a supertrope of cases where hairstyle is used to represent personality, not simply to look interesting or help you tell the characters apart. Compare Stock Costume Traits, where a character's costume indicates profession & status.