Book editing is not the same as writing a book. Neither is academic paper editing the same as writing a paper for school. While most writers do edit, to a degree, and most editors do write, or should, writing and editing require different skills.
In the same way, content editing and copy editing require different skills. Content editing involves revising and improving the way a message is communicated. The editor considers organization, clarity, tone, style, and content. The copy editor (i.e., proofreader) considers writing mechanics: spelling, punctuation, grammar, and usage.
As an analogy, content editing is like improving the design of a car--what works, where a button should be placed, how well the driver can read the dials, whether it feels good to drive, etc. The result is a better car. Proofreader is like being a mechanic--making sure the oil is topped off, adjusting the breaks, replacing the fan belt, etc. The result is the same car, but operating correctly.
Although writers can edit and editors can write (obviously), each has his or her specialty. As we have often told clients, a writer should be most concerned with the content: the ideas, the characters, the information, and so forth. As professional editors, our primary concern is for communicating that content to the reader. We tell clients: "If the ideas are good, we can improve how they are communicated." An editor has a symbiotic relationship with a writer: the editor needs content to edit, and the writer needs editing to improve the delivery of the content.
In a nutshell, this is what we do at Precise Edit: We help writers communicate well and meet their communication goals, whether they are writing a book, a dissertation, a business report, an English essay, or any other form of written communication.