I've been testing web services for 4 years now.
Sometimes it's good to be reminded of the basics when you're explaining JAX-RPC or JAX-WS web services.
Ultimately, when you specify RPC or documental literal wrapped you're stating how the message will be translated to the SOAP envelope that is transmitted over the wire (AKA internet).
In the WSDL you specify the binding or what kind of translation you want in the binding node of the WSDL.
Then that style is used when the message is sent inside the SOAP envelope; specifically the SOAP body.
This IBM article states it well in the first paragraph.