This is a very vague question. your best bet would be to look at school specific forums and see what worked for other people. Every school is different and some weigh them very heavily. A good rule, though, is keep it very efficient and use as little words as possible to get your point across. Anyone can answer a question with 500-600 words but it takes more skill(and quicker for admissions to read) if you write a well-rounded response in 200-250 words.