The purpose of the copyright is to establish the date that you created the work.
That date protects your ownership should someone claim they did the same thing before you did.
That is an excellent and important distinction, and the reason why some people are willing to jump through all of the hoops involved with getting an "official" copyright rather than being satisfied with the automatic kind. Na also made an important point by indicating the difference between copyright, trademark, and patent - something that isn't crystal-clear to everyone.

Ron G.