Everyone who publishes material needs an editor. That's quite a statement, I know, but when you think of it, even the one-person blogger needs to review their work before publishing. Many authors do the editing themselves, but a better idea is to ask someone else, who has not been staring at the page for hours, to look over the material. The more a person or organization publishes, the more a professional editor becomes important.
Here's an example from a well-known coffee company:
This instant coffee package says, "Instant and migroground coffee." It was a new—and secret—process the company was using to create a better-tasting instant coffee, but the coffee is microground, not migroground. If you are very observant, you will have noticed that the "Best Before Date" has long passed. I assume the mistake has been corrected on newer product. Still, wouldn't it have been worthwhile to hire an editor before the first package was printed?