I think, in programming, practical experience (and intuition) is way more important than familiarity with any theory. I mean, sure, it is nice, I guess, to be able to think about functions as "arrows" in the "category of types" and about generics as "endofunctors" (in the same category), and all that; on the other hand, this may be very distracting when you have a real-world problem to solve, and, in the worst-case scenario, it might even lead to a failure - kind of like what happened to a centipede who was unable to move ahead as soon as it started wondering which of its legs it should move first.