Sun signs are a key part of astrology. People who are born under a certain zodiac sign tend to share certain personality traits. Some people are even able to identify themselves through their sun sign.
While the sun sign is the most basic aspect of your astrological personality, it is still one of the most important pieces. This is going to be the sign that carries the biggest pieces of your personality. The rest of your chart tells you about your nuance. The sun sign tells you the big picture.