I may have mentioned this before, but I think it’s worth repeating. It’s always difficult to edit your own work. Getting distance between you and your story so that you can see it through your readers’s’ eyes is not easy. Of course, letting it sit for a while usually helps. If you tend to work on more than one book at a time, this is easier to do. Otherwise, you’re likely to be impatient to finish it up and get it out there.
Even if you have an editor, you really need to go through it again on your own. I have seen too many books that were supposedly “edited” but in some cases I suspect the editor was their dog. Seriously. Partly, this is because there are numerous types of editors. If you’re not paying attention and know the difference, perhaps you’re not getting what you’re paying for. For example, there are simple proofreaders, copy editors, content editors, and line editors. Not every editor will provide all three. Some who are not professional, simply someone with a good eye, may not even notice them.
So, bottom line, if you want your book to be a high quality product, you should go through that final version yourself. The way I prefer to do this is with a proof copy. Yes, a print copy I can hold in my hands and turn the pages. The physical feel of the book in your hands facilitates seeing your story through a reader’s eyes. It’s a different “dimension”, if you will, from an electronic device. For me, it’s also less distracting to underline, highlight, or dog-ear pages that require corrections without losing the flow.