It probably took a lot of hard work, and maybe some research to finish it off.
Publishing is usually the main goal of any writer.
Unless you are a playwright or screenwriter, and in that case you're wanting very badly to see others acting out your characters. Sending a book about the plight of a handicapped Eskimo to an Art Publisher for example, makes no sense. This protects your work by marking the date you wrote it. The registration is good for 5 years and helps prevent someone stealing your piece. You may also want to Copyright it if you haven't already done so.