It is more expensive, and you would not have all Pantone colors available. But, as a printing house, when your customer like for example DHL tells you: "I need cardstock for 1 million envelopes printed with our logo, and it has to be PMS 2035 C red on PMS 116 C yellow." then you buy that exact inks from a printing ink manufacturer and print your cardstock - and if your paper was the correct brightness and the ink manufacturer has mixed the inks correctly, the colors will be perfect on the first attempt.