What am I missing in this? Why would this step not be useful?
Oh, it's useful if the following conditions are true;You have a profession quality display that is properly calibrated and profiled,
You have an accurate printer profile,
You are printing to a pro quality printer,
You are using a "large gamut" working space (Adobe RGB minimum and ideally ProPhoto RGB),
You know how to use soft proofing and understand what it's showing you and,
You know how to correct the soft proofed image so the final print is optimized for both color and tone,
And the final print is viewed under consistent viewing conditions that are in-line (a match) to the display properties.
Soft proofing won't work very well if you;Are using a laptop display,
Using a cheap "smaller than sRGB" display,
Driving the display at 100% brightness and/or at an uncontrolled luminance and/or contrast range (anything above 500/1 is SciFi)...
Don't know how to use Photoshop's soft proofing–including the Display Options (On-Screen) options...
Don't have a standard viewing environment so you have some ideal and consistent print viewing capability.
Look, all I can say is that for serious prints I make (and I'm a pretty darn good printer) soft proofing is the
BEST way to get an image optimized prior to making that first test print (why waste ink & paper if you don't need to?).
Yes, sometimes I'll look at the actual print and decide to go back and make an additional tweak to perfect the final print. Most of the time, I really don't need to make a test print because the soft proofed image gives me the info I need to get an optimal print the first time out of the printer.
The ONLY time soft proofing fails (to my mind) is predicting the image detail on screen.
While Photoshop is capable of accurately displaying tone and color, it's kinda sucks at predicting the image detail (sharpening and noise reduction) you expect to see in the final print.
That's not a limitation of Photoshop so much as a limitation in the resolution of today's displays. When you can get a 30" that has the same resolution of an iPhone 4 retina display (over 200PPI) then you might be able to predict sharpening and noise reduction for the print. Today? Not so much...you either need experience or a test print to tell you the detail the image is capable of producing...