Sun signs represent the will power or personality of the individual. Will power is a term coined by the German existentialist philosopher, Friederich Nietzsche. Nietzsche believed that each person had a unique will to power, to better themselves, to even control the situation around them to contrive whatever results they desired. This led to the term will power. Nietzsche formulated this theory to repudiate Schopenhauer's will to live theory. Nietzsche rationalized that the human being didn't just exist for existences sake, but it existed to better itself, hence the continuous forward growth of man, technology, and industrialization. With this in mind, every human has a distinct will, and this will is what the sun sign helps the astrologer read. This is very important considering that it is the will that determines the path that each human life chooses. Willpower is the freedom of choice, and the results of the choices that you make. The sun sign is not likely to tell who you will like or what you will want but it is very likely to tell you what you might do and why you might do it and how you will go about getting something you want. It can easily help predict reactions and ideas, trends and traits that accurately predict how you might go about your life.
The sun sign is just one more tool, albeit a very important tool, that the modern day astrologer can use to accurately predict horoscopes and most importantly individualized readings. Astrology has come a long way from the middle age carnival shows, the days of guesswork and fraud. Astrology today is a science that uses every available bit of information involving the sun, moon, planet, and stars to accurately predict trends that various zodiac signs have in common.
If you haven't had a reading involving your sun sign and have no idea what your sun sign is, then you've never had a personalized or accurate reading. It doesn't take much time or effort to have a true personalized reading done these days, as the internet has made the world a much smaller, more accessible place. Simply find the sign you were born under where the sun rose at the time of your birth, and combine that with your zodiac, to get an accurate reading of how you, the individual, might react in any given situation.