This question provides you insight into the applicant's personal experiences and motivations. Some people enter the field of clinical psychology due to their own experience with a psychologist or other mental health professional as a child or youth. Some have an inherent yearn to help to others. Some exhibit a curiosity about how the mind works and wish to better understand human behavior. Their response give you a window into their background, personality and work ethic. What to look for in an answer:

Personal experience with psychology

Motivation and passion for the field

Communication of work ethic and habits