Taking into account what time someone was born, and in what sign other planets were in at that given time, date, or region, you can gather insight into someone’s personality. In order to accurately complete a natal chart, a time of birth is needed. However, you can still create a basic chart without time of birth. With these charts, you can get an idea about how someone may communicate, or how they may love others. This, of course, does not take into account how the person was raised.
It may not be an exact science, but it can be used as a helpful tool in getting a better read on someone.