Another is that they'll do their job a lot better if you give them as clean a manuscript as you can. (chriskridler.com)
Other authors have honed their grammar, lexical skills and language knowledge to help them produce much cleaner manuscripts. (feedspot.com)
I'd rather my editor and proofreader start from as clean a manuscript as possible, and I also learn each time I go through this exercise. (thecreativepenn.com)