What does the chronology of heavenly stems and earthly branches mean? What are the advantages of this chronology?

For example, Jia Zi is the first year, Ugly B is the second year, and Bing Yin is the third year ... Sixty years is a week. Week after week, starting from the year of Jiazi, starting from the week, and starting again and again. It is said to have a deep meaning. It's just that people in feudal times don't like truth, and truth is only used for fortune telling ~ ~