I'm not an Editor nor do I play on on TV. However, as a writer I see the tremendous value in editing. I highly recommend people hire and develop a close relationship with an Editor. They can do so much to help shape your book and your writing. In my opinion, a good Editor doesn't rewrite your book. They help YOU write it better. Your unique dialog, characters, plot, settings, voice, and narrative are what you are bringing to the table. An Editor helps by getting rid of the "clunkiness" that plops up in all of our writing. You should be catching most spelling errors and some grammar errors with your word processor's spell check and grammar check. An Editor shouldn't have to waste time correcting spelling and grammar errors--at least not the easy to catch things. Of course these tools aren't perfect and another set of eyes are helpful to catch words like "united" that get written as "untied." I made such a boo boo once in a fund raising letter I had written for an organization. I didn't catch it until weeks later after dozens of letters had gone out. Software has its limitations.