In universities, what are the advantages of having a second department affiliation?
Sometimes, a second affiliation has real administrative meaning, for example if a professor's teaching duties are divided between two departments.  In other cases, a professor's duties are in just one department, and the second affiliation is either just an honorary matter (saying that the second department regards him as respectable in their field also) or possibly (depending on university rules) enables the professor to officially supervise dissertations in the second department.