what is the importance of the doctrine of precedent?

Answer 1

There are two types of law, statute and precedent.

Both the Australian and US legal systems are derived from the English Common Law. Under this model, the legislature writes prospective general laws, based around expectations and future events, and the courts interpret those laws to specific situations and applications by resolving specific controversies when they arise.

Those rulings that arise out of specific cases and controversies are called common law. Every time a court case is cited for a particular rule, that's an application of the Common Law. All of torts for example, as well as most of American criminal procedure, primarily are based on common law, rather than legislative statute.

The doctrines of precedent and "stare decisis" (literally, "let the decision stand") require courts to follow past decisions. This ensures that the same set of facts achieves the same outcome during later trials.

If prior decisions (precedent) were not binding, then judges could ignore those decisions, and make any ruling they want. There'd be no consistency.