Soft proofing. If the concept is to simulate on screen what you should expect when you print, how come people don't just enable "View Proof Colors" immediately upon entering Photoshop (assuming you intend to print)?
Rather, every time I read/research this topic, basically you spend all of your time adjusting the image to get it looking great on screen. Then you enable proofing and see how terrible it looks on screen, then readjust everything you adjusted before, then print and hope for the best.
My knowledge of this is fairly limited, but I have three possible theories:
1) I am completely mixing things up and scrambling different, unrelated things together into something that only exists in my twisted mind.
2) As backwards and frustrating as it is, this is simply how you do it (which there must be some important reason for).
3) Nobody actually uses soft proofing and I shouldn't either.
Take your pick, ladies and gents!
Assuming you have a properly color managed workflow. . . you edit the base image till it looks good to you on your screen. Then, when it comes time to print, you load the print profile and then softproof the image to see what it will look like 
