There is no direct correlation between the colors on your screen and the colors produced by a printer. You can prove this to yourself by taking a scanned image or digital photograph and printing it on several different color printers. Each printer will produce slightly different results. The same graphics image when viewed on different monitors can also look dramatically different. These color differences are more than just a nuisance.
Some companies are very particular about shades of color.
The cars are all one specific shade of red. Look through a clothing catalog such as L. L. Bean and you see garments with such shades as burgundy, plum, crimson, and rose. For these types of companies, accurate color reproduction means money. This is where ColorSync comes in. A profile contains information about how the device renders colors.