There are schools that require an applicant to submit a Statement of Purpose instead of a PS, the thrust of which is to present an applicant's goals in terms of what major to pursue, what research direction to take, and other specific study and career plans, if any. Therefore, in this case, you are required to submit a similar essay but with greater emphasis on your specific study and career plans. Most applicants are confused with the difference between a PS and a Statement of Purpose. This is not to say, however, that a PS cannot be a Statement of Purpose and vice versa, because as you will discover in the next section, these two can actually overlap depending on the outline you have created.
When you allow a fresh set of eyes on your admission essay it is almost as if your personal statement is getting practice. After all, your statement will ultimately end up being read by one or more people while your application is being reviewed so it makes sense that a well read personal statement should do better in its final stages. Why have the reviewers catch the mistakes that someone else can catch beforehand? It is far better to catch a small mistake that can cost you admission, before it actually has the chance to cost you.