Working according to standards or specifications like PSO, SWOP or GRACoL has several advantages for printers. On highlight are similar proofs from different systems. Proofs from the client or in-house proofs have the same color appereance. If the printing house communicates, that proofs from clients have to confrom to PSO, SWOP or GRACoL, this proofs must contain a vendor independent color bar. This allows a verification and identification of bad proofs before they are coming to the press.
As applications like e.g. Adobe Creative Suite are using out of the box color settings, which are conform to PSO, SWOP or GACoL, it makes sense to optimize the printing process according this specifications, This is the most secure way to match in print, what the customer sees on his (hopefully) calibrated display.