In a court of law, a precedent is important because it gives the judges a base guideline to work from when deciding the outcome of a case. Many of the precedents laid down for the courts to follow have been around for over 200 years.
Precedents are often used to appeal or overturn previous judgments. These cases go from the standard court to the appeals court where precedents are often cited as the grounds for a ruling to be overturned. The precedents set forward are not binding in legislature, and legislators can pass laws to overturn rulings that are unpopular. Unless the Supreme Court says that the laws are unconstitutional, they take the place of the precedent that was previously used in its place.