I worked through a popular Introductory Category theory text. Did all the problems and made sure I understood everything in there really. It became clear by the end why some mathematicians like category theory. It lifts some results in certain areas to a higher level of generality.

As for me it helped me with understanding some of what was being discussed on r/haskell. It didn't help one iota getting me a Haskell job though, failed every Haskell code pairing I've done.