In the UK there are copyright libraries - you must give a copy of your work to these libraries if you want the government to prosecute copyright for you.
The British library (equivalent of LoC) is one.
It may have changed, but to register your copyright, you send (I think two) copies to the LoC with the registration. The issue isn't whether LoC gets a copy, the issue is their ability to backup or transfer the information in the event the media deteriorates or for other risks.
