Not specifically ZX, but rather any non-trivial technique for modeling quantum dynamics (or some subset of such dynamics) is extremely useful: it lets you study

Not specifically ZX, but rather any non-trivial technique for modeling quantum dynamics (or some subset of such dynamics) is extremely useful: it lets you study what is the boundary between classical and quantum algorithms. Consider that I am excited even about the worst case scenario: I am a researcher working on building quantum hardware -- if one day techniques like these show that you can actually simulate a complete quantum computer efficiently in a classical computer, then my whole field will die. But that would be a monumental win because we would have learnt incredibly deep truths about the laws of math and nature. Or more realistically and practically, currently such techniques let us model small parts of the quantum hardware and let us make informed decisions about how to proceed with building it.