You have a document for copy edit. It's a long one. A report, a review, a proposal. You've worked hard on it. It's been reviewed and edited and rewritten, and you've read it over so many times just looking at the words makes your head hurt. Finally, though, it's ready for a copy editor.
And your copy editor needs instructions. They need to know your style guide. Whether you want light edits or heavy language modification. They need to know what elements you're most concerned about, and what should get a less comprehensive touch. By all means, tell them your preferences. But there's one thing you should never, ever tell your copy editor before they get started on your work:
"This section and that appendix doesn't need copy editing, so don't look at them."
There's lots of reasons you might say this. For one, maybe this is your copy editor's second pass over the document. Maybe they've already seen most of the copy and you just want them to look at the more recent changes. Or maybe the section in question is quoted or reprinted text, so changes to wording or punctuation shouldn't be made.
In which case, yes, your copy editor should know that's the case. Tell them that. But never go in assuming that your copy editor doesn't even need to look at those sections. Never assume you can save time or money by having your copy editor skip entire pieces of your manuscript wholesale.
Here are some things that can go wrong if your editor skips a section:
The section can be out of place logically with the surrounding text.
The section can have language differences (capitalization of terms, for example) that are jarring with other sections if they're not standardized.
The section's formatting may have been thrown off by changes in other sections, and it needs re-adjusting.
The section may have leftover mistakes that weren't caught the first time around.
The section may have redundancies with other places in the document that could have been eliminated if the editor had read it over.
All of this adds up to your manuscript looking like a patchwork quilt that's oddly stitched together by diffferent authors at different times, and like nobody's had a look at the whole to make it cohesive. That's what a copy editor is for. To tell them to skip a bunch of the document is to instruct them not to do their best work.
Don't shortchange yourself and sacrifice your credibility for the chance to pinch a few pennies. Get the quality, comprehensive look your document deserves. I look at every word, every time, and it's always worth my clients' investment.