Audience
When writing an SAT essay, it is very important to think about the audience. This is especially true when writing for an audience that is from academia. The people who read and grade the essays want to be able to clearly read the essays. The more hurdles they find with grammar, organization or even penmanship, the higher the chances they will give a lower score.
Most writers struggle with forming clear ideas and expressing them with words. Graders of the SAT essays look for these types of writers and can even enjoy giving them a perfect 6 after reading a lot of other inferior essays. This is why presentation and thinking about the audience is so important for getting the highest score possible. By knowing what the test grader wants to see on the essay, it is easier to construct something that will make them happy to give a high score - even a full 6.