What would happen if I placed my manuscripts in the Public Domain?

Mike Taylor, Computer programmer with Index Data, palaeontologist with the University of Bristol, and advocate for open access, open data and open source on the Copyright status of work by the U.S. government and its possible influence on scientific publishing towards open access:

So journals and publishers are already set up to deal with public domain works that have no copyright. And that made me wonder why this option should be restricted to U.S. Federal employees.