It's a matter of opinion on what should happen if the PU is decleared but not used. Imagine another scenarion when you have more than one PU defined in your persistence.xml and you use only one of them? You might be surprised to have unused tables created or even worst PU loading fail because that other PU references a datasource that had not been even configured.
Regards,
-marina
[Message sent by forum member 'mvatkina' (mvatkina)]
http://forums.java.net/jive/thread.jspa?messageID=280601