Proofreading is the last aspect of the writing process before your book gets in the hands of readers. Proofing is necessary no matter what you intend to publish. It is a painstaking process where the text is scrutinized to find errors. Every aspect of the book must undergo this process. This include the cover. No matter how great your story is, your readers will get turned off if your book is riddled with errors. It is always a good idea to have someone proofread your book. A pair of fresh eyes will often catch the errors you missed. Good luck and happy writing.