I think that these posts about editing should probably be taken as a view of my thoughts on editing as it evolves over time, so it is probably a good idea to ensure that you have read all of them (links top right).
I've been thinking about this one for a long time, and as I specialize more and more in story development and do less and less copy-editing, I think there are a couple of lines that I can draw fairly clearly on the subject of what you should not expect.
To get copy-editing out of the way: from a copy edit, you should not expect your manuscript to be error free, and conform perfectly to every style guide. But you should expect errors to be few and conformities to be maximized.
For a content edit, here are a few things that you shouldn't expect, after your edit has been completed:
1. All content editors agree that your manuscript needs no further editing.
The truth is, your editor might think that the manuscript needs further editing, but doesn't want to overwhelm you. A content editor is not just working with your manuscript. He is working with you. Even an experienced writer can still learn and improve, and working with an editor is a good way to stimulate this improvement. So an inexperienced writer might, not to put to fine a point on it, have a lot to learn. A responsible editor may well chuse not to draw attention to all the problems, because it can end up looking insurmountable. Actually this doesn't happen all that often, but it is worth being aware of it.
More often, different editors will have different preferences and priorities, and what you chuse to do to solve one problem might be considered a new problem by a new editor.
Editors' preferences might run to your turn-of-phrase or even vocabulary choices. Editors' might prioritize, narration, characterization, plotting differently. This is why I've already blogged on chusing the right editor for you. Complete your rewrite, your editor might tell you it's all good, you send it to another editor and he might tell you something completely different. Hence point number 2:
2. Your editor will tell you when your manuscript needs no further editing.
Content editing is expensive, time-consuming and its results are uncertain. Even though those who have tried a professional content editor generally want to do it again and again, it's worth looking for alternatives. Discussing your work in writer's groups is good, as is using a panel of beta-readers. I think that a content editor brings something else to the table, though, and that is a service tailored personally to you and your book.
Even so, only you can decide when your book is ready for publication. I think if you use an editor and are not satisfied with the draft you do afterwards, but the editor thinks it's good, it probably means the editor wasn't a good match to the book, or to you, or both.
3. Everyone who reads your book with think it is great, and
4. You will sell loads of books because your book is great
It may seem obvious that these two are false, but it is worth preparing yourself mentally for the reviews that say: "this book seriously needs editing!".
And indeed, mentally preparing yourself for not selling many books.
It's the subject of much curiosity and discussion, that the quality of a book doesn't seem to be much of a factor in its (initial) success. That seems to be largely luck. Once the book is established, the better books will continue to make good sales for longer, we hope.
Tangential to these two is what is, for me, the bottom line of what not to expect:
5. Your book will be great because your content editor is great.
If you have a great content editor, she will have done a great job at finding the problems and opportunities, documenting them, communicating them to you, and suggesting what you should do about it. However, she won't be the one rewriting you manuscript. That will be you. No matter how good your editor is, your book can only be as good as you can make it. I believe that if your editor is great, then you can make your book a whole lot better with the editor than alone, but it's still you the limiting factor.
I find I can be very open about this with my authors; most of you think you are worse than you are; all of you are trying to become better. I believe that working for authors who are humble but ambitious, keen to learn and hardworking, is what makes me become a better editor. Since I work with lots of authors, while most authors work with two or less editors, I reckon I get the better side of the deal, which is why I advise all writers to try more than one content editor: even if the one you have really suits you, you can learn a lot by working with someone else from time to time.