Some writers are unnecessarily paranoid about sending out their material without a registered copyright. As I have said, they have automatic protection, whether it is registered or not. Although there may be rare exceptions, editors/publishers do not steal the material that is submitted to them. It would not be worth the risk to their reputation. Even stealing a writer’s idea is usually counterproductive, since it is an author’s unique connection to or treatment of the topic that makes most ideas valuable to the publisher.
Some writers believe that if they complete a manuscript and mail a copy to themselves, it will prove that they wrote a particular piece at a certain time. This has become almost an urban myth. Since postmarks can be falsified, such a letter will not stand up in court. If you have a valid reason to protect your material—as indicated above—then spend the $45 for the copyright registration.