It's very valuable if you're printing a single spot color on something. Instead of doing a cyan pass, a magenta pass, a yellow pass, and a black pass, you can just do a black pass and a pass of your spot color. Despite Pantone being a more expensive ink, you may end up spending less money because it allows you to simply use less ink, and fewer resources.

Not to mention when you supply a Pantone color, you will get exactly that color, no matter what print shop you go to (As long as they pay for Pantone inks).