None of the Ivy League universities (Brown, Columbia, Cornell, Dartmouth, Harvard, Pennsylvania, Princeton and Yale) requires the SAT essay any more.
Stanford strongly recommends writing the essay as does Georgia Tech. West Point requires it.
About 10% of US colleges and universities require the essay. The less prestigious the college, the more likely it does not require the essay.
Unlike the multiple choice math and writing sections of the SAT, the essay score is subjective based on the judgment of two readers (possibly two machine readers). A perfect score is 8 based on each of the two readers giving a score of from 1 to 4.
The score on the essay is based on one written response to one essay prompt, unlike the scores on the math and writing portions which are based on dozens of questions, each with just one correct answer.
Factors that could influence your score include your reaction to the subject matter of the prompt, your familiarity with the culture and writing style of the prompt writer, and who grades your essay.
The likelihood that you will achieve a perfect 8 on the essay is one percent, according to an analysis of College Board data by Compass Education Group.
The essay you need to write is judged on three criteria: how well you summarize the main points of the essay; how well you identify and analyze why the prompt persuades; and how well you write your essay in English). The hardest of these three criteria to score well on is the analysis of the prompt’s persuasive techniques.
More than 80% of test takers receive a score of 4, 5, or 6 on the summary and writing aspects of the essay but receive a 3, 4, or 5 on the analysis, according to Compass Education Group. Readers/scorers of the essays seem reluctant to give the highest or the lowest scores. So like a bell curve, most scores cluster in the middle range of possible scores.
You can think of the essay scoring as like the scoring of competitive gymnasts, with each athlete’s score decided somewhat subjectively by the judges. If you score a 6 on your essay and your friend scores a 5, does that mean your essay is better than hers? No. What if you score a 6 and your friend scores a 4? Yes, in that case, you probably did write a better essay.
If your college choices don’t require an SAT essay, then you should probably skip writing the essay and lose no sleep over that decision. But if you are an excellent writer, then you should probably write the essay. If you do well under test conditions—50 minutes to read, understand, and analyze a prompt, and to respond in essay format in near perfect English—the advantage is yours.