Thanks to all, with special thanks to artd. I have been enlightened.

OK, point taken about not using the monitor profile for the working space. But how does Photoshop know that I've created a custom profile for the monitor if I don't enter a thing about it on the PS GUI?

You can select a profile from the RGB drop-down menu in that window. I first create a profile by using a colorimeter to calibrate my monitor, and then I see the profile's name in the drop-down. You can alternatively select a default profile, but if you calibrate your monitor, you won't want to choos...

I edit and print a lot of images with Photoshop. I understand why I need to calibrate my monitor regularly to have confidence in my editing and printing. What I don't understand is why I need to identify the monitor profile to Photoshop in the Color Settings window. I've been told that the monitor p...