While the writing section of the SSAT is an important section of the test, it will not be factored into your overall test scores. Rather, a copy of the essay will be sent along with your scores to the school(s) that you are applying to.
Although the writing sample is not directly scored, the writing sample will be used as a part of the admissions process. Many admissions directors describe the test’s essay section as one of the most important parts of the application, indicating a student’s writing ability, interests, and personality with no external influences.
You can read more about strategies for the essay section here.