Subject Tests usually referred to as SAT II last for one hour, content-based tests that allow you to showcase achievement in specific subject areas where you excel.
SAT Subject Tests makes you to differentiate yourself in the University admission process or let people know your readiness to study specific majors or programs in University. In conjunction with your other admission credentials (your high school record, SAT exam scores, teacher recommendations, etc.), they provide a more complete picture of your academic background and interests.