This exactly what I mean by: sometimes provides you with an additional insight in the structure of the stuff you are researching and makes it easier to notice

This exactly what I mean by: sometimes provides you with an additional insight in the structure of the stuff you are researching and makes it easier to notice and classify similarities between different kind of structures I just tried to avoid the notions which average HNer is unlikely to know, and understanding them takes too much time. Anyway, I have yet to see a deep and nontrivial result in a pure category theory, and mind you, I have the Mac Lane's book in front of me. Most of it is easy symbol juggling which only result in something interesting when you think what it means in context of concrete structures.