Essays are used to learn more about your reasons for applying to the course, university or company and your ability to benefit from and contribute to it. Your answers will let you state your case more fully than other sections of the application, and provide the evaluator with better insight about you and how you differ from the other applicants. In marginal cases, the essays are used to decide whether an applicant will be selected. The purpose of the admissions essay is to convey a sense of your unique character to the admissions committee. The essay also demonstrates your writing skills as well as your ability to organize your thoughts coherently.
Use your best judgment on who you decide to ask - there is no set formula for who should be your recommenders. We know it is not always possible to have a direct supervisor write your recommendation – we would not want you to jeopardize your current position for the application process. Look at the questions we are asking recommenders to complete. Find people who know you well enough to answer them. This can be a former supervisor, a colleague, someone you collaborate on an activity outside of work. How well a person knows you should take priority over level of seniority or HBS alumni status.