In addition to judicial review, the supreme court has the power to overturn its own decisions. why is it important for the supreme court to possess this power?

It is important to realized that judicial review is not an unlimited power. Although the supreme court can strike down laws and actions, the court depends on other offices of government to apply court decisions. In short, the court lacks the power to enforce its own decisions and needs federal and state politicians to interpret the court’s ruling and carry out the enforcement. Like anything else in life, interpretation and enforcement of court decision can be conscientious or lax, good faith or bad faith efforts. In addition, amendments can be added to the constitution through a process involving proposal by congress and ratification by the states. This means that if the court strikes down a measure passed in the form of law, the very same measure can be rewritten as an amendment to the constitution and if proposed and ratified, it stands as a part of the constitution and is outside the realm of judicial review. 

Dhope it