Answer:
poems allow for a lot more creative freedom and can include a wide range of possible structures and techniques. A composition makes logical points that should be clear to anyone who reads it.
A composition is the craft, the arrangement of the text whereas an essay has a strong nonfiction characteristic to it. While essays can be creative, there are more academic expectations for its prose form and realistic content. A composition can more readily dance on the line between fiction and nonfiction, whereas an essay must be more subtle it its subversion of nonfiction status.