A good editor will give it to you straight, and tell you what they like and hate about your writing. They will tell you that you need to change this, or that one scene does not work with the book. They are necessary because you can read your own writing a hundred times, and still miss all the typos. I know that I do, and I still have to read through books I am editing several times to make sure that I have not missed anything.
The question I am asking in this post is, should your editor be a friend? The reason this is a question is because lots of Indie Authors prefer to use their friends as editors instead of paying someone. This can be a mistake if you friend is scared to be critical of you, and also if they are not going to really edit your book. If they just skim it and tell you that it is brilliant then they could be missing typos all over the place.
That being said, sometimes a friend is also an English major and she nails the edit job for you. You really just need to think about who you let edit your book, because especially when you are an Indie Author reviewers can be really picky and sometimes will dismiss a book on the first typo they find. This is not fair of course, because everyone makes mistakes, but it is still a sad reality.