If you are serious about getting published, then yes, you most likely could benefit from an edit. An edit is a learning experience for an author. Due to the competitive nature of the industry, the literary standards are growing and an edit offers your book an edge. A professional editor can point out where the manuscript is underdeveloped, where it feels lifeless, or where the book overdoes certain elements. Agents and publishing house editors typically know within the first few paragraphs if a book has been edited or not. A professional editor knows what to look for and what hooks an audience; an editor is the second pair of eyes that every book needs. Also, there are editorial standards that only those involved in the industry would know, even if you did get high scores in high school English class. Consider your manuscript as an investment—it takes effort to get the text where it needs to be in order to achieve the high standards required by publishers. By cutting corners you only hinder the potential of success.