The amount of money you can get if someone violates the copyright is much more limited if you don't register. https://www.copyright.gov/help/faq/faq-general.ht

The amount of money you can get if someone violates the copyright is much more limited if you don't register. https://www.copyright.gov/help/faq/faq-general.html#register https://www.copyright.gov/help/faq/faq-general.html#register