Many people don't know what is meant by a developmental editor.
This is because the word isn't always used to describe this task.
As with many jobs, the role of a developmental editor is often absorbed by other editors.
Whatever the title, the job of the DE is to shape the book or story.
Does the story make sense? Does the pacing work? Is there consistent POV? Does the tense randomly change? Do the characters make sense? Do their names or attributes change for no reason? Is there a conflict? Are there too many/not enough characters?
A Developmental Editing service does NOT include Copy Editing. That's totally different.
Developmental editing will sniff out those tricky things that slip by a writer who has been staring at his or her own work for too long. Once a writer has hammered through a few drafts, it can be difficult to remember who did what and when or if they did it at all?
A developmental editor will flag scenes, characters, and more through the comment bubbles. There might be dozens of suggestions to strengthen and shape the work to its maximum potential.