Why is it so important for the U.S. to have a the Supreme Court? There are many different reasons for this such as declaring a law unconstituional or even hearing a case that the decision has been appealed that a court case gave. The Supreme Court is also decided many cases that helped the U.S. But the main cases the court has heard in my opion are " MALBURY V. MADISON", "FLETCHER V. PECK", and " MARTIN V. HIUNTER'S LESSEE".