I pick these two papers. The first is literally about adjunctions pertaining to combinatorial species whereas the second devotes an entire section to reviewing the theory and stating results that it uses in a way that I don't really understand. I'm going to read the first paper though because it's relevant to my interests :)
Rajan. The adjoints to the derivative functor on species
https://www.sciencedirect.com/science/article/pii/0097316593...
Panagiotou, Konstantinos; Stufler, Benedikt; Weller, Kerstin. Scaling limits of random graphs from subcritical classes.
https://projecteuclid.org/euclid.aop/1474462098
The fact that I have to go rummaging around for these examples kind of proves your point, doesn't it? I don't think category theory will lead to any fantastic new results in the fields we're discussing, but the bar is quite low for it to be useful as an organizational tool.
^ I searched for the word functor of course! :)