Soft proofing can save time and money by reducing the number of prints necessary to get the desired results.
Performing a gamut check lets you see what colors are out of gamut for your printing device, which can reduce unwanted surprises and costly reprints.
The key to accurate color-managed printing from Photoshop is making sure that color management is applied only once by Photoshop, not by the operating system or printer driver.
Photoshop's Assign Profile command can be used to change the embedded profile in an image or to assign a profile to an untagged image.