Alter a project while the print screen is open.
Often I enter the print screen and take many steps setting up a print then need to make a small adjustment, such as hiding certain tracks or markers or changing colors, and have to close the print screen, make the changes and then reopen print to make all the adjustments that were just set up to print the next map.
Jack Carlson commented
After adjusting all of the label text on the map, I open the print screen and find that some of the label text has moved to the next line. I have to go back to the map and tweak the label box size so the text stays in place. Being able to make adjustments while the print screen is open would be nice.