Ok, no one really replies, so I will try to...
You mean a real life example of why do you need the JNDI ENC when defining a reference to another EJB / resource / persistence
unit / etc.?
The below post is just my point of view - it doesn't have to (in any matter) reflect how it really was.
I guess it's because of the backward compatibility.
I can just suspect that in former days there wasn't an easy way to access the 'injected' EJB reference from another EJB. That's why they need to define (in DD) in what JNDI location the reference will be available for the given EJB.
Right now you can still define in what ENC JNDI context you would like to put your injected EJB reference to be able to look it up directly in one of your business methods. Then again, I guess that nowadays you can use the @EJB, @Resource, etc. (not mentioning the CDI!) so I can't think of of any real use of the directly accessing the ENC using JNDI aside from integrating with some legacy code.
Did it help you in any way?
Cheers!