Good Interview Question

From the GWT Developer Guide:

Polymorphism
GWT RPC supports polymorphic parameters and return types. To make the best use of polymorphism, however, you should still try to be as specific as your design allows when defining service interfaces. Increased specificity allows the compiler to do a better job of removing unnecessary code when it optimizes your application for size reduction.

It'd be interesting to have a candidate analyze and explain that para. Especially the part about specificity and unnecessary code. I don't think it will matter if the candidate knows GWT.