Most new writers hear the word “editor” and think of the acquiring editor of a traditional publisher who will call you with the news that the publisher wants to buy your book, send you the legal documents to sign, then lead you through the process of rewrites until the book is ready for prime time.
Editors, however, are diverse in skills and roles in both traditional and self-publishing. If you want someone outside of the traditional publisher to help you create a publishable book for either traditional publishing or self-publishing, you need to look for different types of editors.
First, you need a developmental editor who will look at big picture things like plot, structure, characters, facts, etc. of the entire novel. Here’s where those pages of rewrite suggestions appear.
Once you and the developmental editor think your work is sound, you will need a line editor or proofreader who will do a close edit for grammar, spelling, and clarity. Some fact checking may be added to that mix. At this point, the book may be ready to send to a traditional publisher.
For a more in-depth look at this part of the process, read Sandra Wendel’s article on the subject. https://www.janefriedman.com/the-differences-between-line-editing-copy-editing-and-proofreading/
For self-pubs who will publish to places like Amazon Kindle, a format editor may be worth the cost so your manuscript doesn’t have unexpected format issues as it’s translated.
NOTE: Good writing teachers will help you perfect the small elements, critique partners will help with the bigger picture as you work, and beta readers are your manuscript’s final look, but it’s the professional editor who can help you polish your work to a pro standard so don’t skimp on paying the pros.