Students who wish to take the SAT in August must register asap, as historically there have been a limited number of test sites in NYC for the August exam. Register early atthis link.
Many colleges consider SAT scores as part of their holistic admission and placement decisions, and your score is a valid way to show what you've learned. Most juniors take their first SAT in the spring, and many take it again in the fall of their senior year to improve their score. It can help you keep your college options open, demonstrate your unique strengths, and even qualify for scholarships.