One of the biggest struggles I've experienced since indie publishing my first novel, Becoming His, was people assuming that it would be an unpolished mess of my own thoughts. You see, when I elected to indie publish, not a single platform that I posted my book to asked me if I had made the right decision and had the book professionally edited--not one. Amazon will notify you of errors that they find, but more often than not it's the name of a character rather than a legitimate error.
You'll notice I said "the right decision, and had the book professionally edited." Clearly this is my own opinion, but to me this is an essential part of the publishing process. I think of it like making an elaborate meal, and then burning or under-cooking it because you didn't know how to properly cook it. Sure there might be some decent bites, but overall the flavor isn't cohesive, and there are inconsistencies as well as large distractions. And this "meal" is something you don't spend a mere few hours on, it's months of work and research and revisions.
I go through my completed manuscripts three times before they reach an editor, and while I can be a pretty decent critique partner for my author friends, I can assure you my returned manuscripts still have a mess of corrections when they're returned to me. For some, this is a very disheartening reality, and while I sometimes feel a bit overwhelmed by the edits, I've always loved the process because I continue to learn and grow with each book.
My two cents on why EVERYONE needs an editor:
1- An author knows their characters and storyline very intimately, making it easy to forget explaining some of the crucial details to readers.
2- While beta readers are generally used to help with plot issues, editors are another wonderful resource to ensure that all of the dots you've dropped throughout the story connect at the end.
3- English is a crazy language. CRAZY! There are so many rules and style guides that it's impossible for anyone to know them all, which is why there are people that went to school and studied editing. They know that you don't capitalize aunt when it's proceeded by a pronoun, and all kinds of things that many don't, in addition to cleaning up obsessive commas, and pointing out when you're telling a reader something versus showing them the scene. You see a doctor when you're sick. You should see an editor when you write.
4- You want to put your best foot forward. Whether it's you first book that you're publishing or your tenth, you will have new readers, and you want to be sure to show them the best side of yourself and your writing abilities.
I realize finding an editor is hard. It's really hard in fact. Below you'll find a post I wrote about how to find an editor, and some tips and questions I suggest asking. An editor is an expensive investment, so be sure to go into things with both eyes wide open.