It is useful for anything from bringing a doomed article back from the brink of damnation to improving upon a completed article written by Jesus himself. It is an author's job to improve the article based on the feedback given. Please don't make a Pee Review request solely to show off your work with no intention of changing it. If you are not going to take the criticism to heart one way or the other, don't bother requesting it. If you request a review, you can add the template to the article to make sure nothing happens to it until the review is finished.