[Hamuko]

And then you'd probably not get what you expect since your CMYK printer isn't calibrated like the print shop's printer is, despite having the same kind of paint.

[seba_dos1]

You get what you want, because you use a Pantone color to match it. Otherwise we wouldn't be having this discussion at all.

However, for Photoshop specifically, the only use of that information is to display an RGB approximation.

(although with uncalibrated printer you'd be screwed one way or another, I guess)