Answer 1

Lots of students take SAT more than once to improve the scores. Given many colleges superscore using highest of each section across all your attempts, retaking the test can increase your superscore. Having said that, according to the College Board:

• 55% of juniors taking the test improved their scores as seniors 
• 35% had score drops
• 10% had no change
• The higher a student's scores as a junior, the more likely that student's subsequent scores will drop. The lower the initial scores, the more likely the scores will go up.
• On average, juniors repeating the SAT as seniors improved their combined critical reading, mathematics, and writing scores by approximately 40 points. About 1 in 25 gained 100 or more points on critical reading or mathematics, and about 1 in 90 lost 100 or more points

​Your SAT score report provides additional information based on your actual scores. 

Answer 2

Retaking the SAT depends on many factors -- 1. what is the total score earned on the first administration ? 2. do you want to improve a specific section such as math or critical reading ? 3. are you trying to earn a better score for scholarships reasons or admission ? 4. how close are you to your desired score? 5. do you feel you underperformed for a medical reason, a personal reason or you made scoring error ( skipped a question but marked the next answer in it place) 6. did you feel unprepared with little or practice? These are factors that need to be considered and each student's needs are different and each situation is different so there really is no set answer -- one size does not fit all. A low score could an indication of almost anything and it would take some careful review of the answers to make a decision. I wish I had a more concrete answer, but deciding to retake the SAT is a highly personalized decision. Best wishes to you and much success for the year.