You Need Personalized Coaching: In some ways, your developmental editor will serve as your writing coach, guiding you and pushing you and helping you in your journey from start to finish of your first draft. It beats struggling to do it on your own for 4 years.
You Need Help with Your Plot and Character Development: Sometimes, coming up with fluid, interesting characters who drive your story can become a difficult task. A developmental editor will help you to develop your plot, theme, mood, pace and so much more to bring your story the life that it lacks.
You Want to Save Time: When hired early on in the writing process, a developmental editor can save you the good amount of time you'll be wasting on rewrites if you are struggling and choose not to hire one.
You Want to Saves Energy: The writing process can be a tedious one for a writer who lacks direction and guidance on how to get to the end of a story (or how to start). If you have no idea how to get from point A to point B, you'll find yourself frustrated, expending energy and effort on unnecessary editing and rewrites before you even hit the "End" button on that last page.
A developmental editor can help you in ways that will cut down on your frustrations and your moments of doubt and fear, and lead you safely and sanely through the process, and to the end. If you are struggling to get started with that book idea that has been passionately burning inside you, or you have started and feel stuck, or are wondering if your story even makes sense and if it will sell, then consider hiring a developmental editor. Doing so will save you so much in the end, leaving you with a publish-ready manuscript by the time it reaches a copy editor's desk. At which point, all you'll probably need is proofreading and nothing more.