Once your creation has been fixed in a tangible medium of expression the copyright on your work is protected by copyright law.
By registering your copyright you will have irrefutable proof of first ownership of your intellectual property.
This proof can be used in a court of law in alleged cases of copyright infringement. When faced with an alleged case of copyright infringement you need this proof.
Proving the date of creation can be a problem. Copyright registration can make the proof on this point a lot easier. By registering it you will have an individually numbered certificate of registration of copyright relating to that particular copyright work.