I think this is an XYZ question. The interface design question is backwards.

Instead of asking, "What kind of information does this subroutine return?" he's asking "What kind of information does the caller want?"

The only place where this question might fit is when you're replacing an existing subroutine, and the interface already takes context into account. (Pointing out wantarray takes care of that.)

In short, I'm terribly confused by this question altogether, and very curious as to what lead to it.