It is an age-old tradition in Hindu families where the horoscope matching is the fundamental step before proceeding with any marriage proposal.
It is really one of the great tools the ancient sages have gifted us. Astrology deals with nature of the persons and it is obvious that it can help to a great extent in deciding marital compatibility. It perhaps is the only tool to find out how the couple can adjust and adapt to one another for the whole life ahead, since Hinduism believes in the concept of 'Single Partner' for the whole life.
Since everything pertaining to the couple - their health, family, wealth, attitude, children, parents, profession, flexibility.... and so on can be judged from their horoscopes, perhaps it is the best method to match the compatibility when done in a proper way by a wise person.