Why can't it be both? I think that you're right, the technique you describe is good for exploring your own maps, but I also think it seems to work for figuring out where the territory continues but your maps end.

I also think I didn't do a sufficient job of explaining that my "exploring the depths of knowledge" take pertains more to your "The sky is blue" example than your "This book is awful" example (i.e., one that can be answered with fact, rather than opinion.)