There's a couple of situations where you might use a Pantone or spot colour. One option costs a little more and the other costs a lot less.

Adding a little extra

Adding a Pantone colour to your normal CMYK is a great way of achieving colours which simply are not possible with 4 colour process printing. The example above from the Print Handbook is a great example of this. The Pantone here is a vibrant red which simply wasn't possible using just CMYK inks.

It's also possible to use a metallic or fluorescent ink which CMYK can get nowhere near in impact. It's a great way of adding an extra little something to your project.

Adding an extra colour is not as expensive as you might expect either. Here's a quote from Centreprint for printing 10,000 leaflets. In CMYK they'll cost £317. To add a spot colour would cost an extra £38. Not bad at all.

One colour job

If you or your client are on a tight budget then using a Pantone spot colour for a one colour job can be a great way to save money. The same specification as the above quote, but this time printed with just one colour would cost £158.

Here's a great example of how to use a single spot colour. In this case it's a metallic Pantone.