PK can be used on any paper. MK, not so good on glossy. Dilutions use less ink, so if you use PK for that you'll have an inkset that you can use for any kind of paper if you have 100% PK and 100% MK positions in your printer with your custom dilutions. Super flexible because you can print on any paper finish. MK should also get you a denser black which would be more desirable instead of using PK for everything. That's roughly what I do but I include that toner I was talking about to shift the tone blue.