As I mentioned a couple chunks ago, you can restrict the hours when people can actually print to a particular printer. You do this by setting the printer's hours of availability.
Continuing the Photo/Text print example from the previous chunk, you might expect the Photo Printer to print much slower than the Text Printer because of its higher resolution (and, for 95% of the printers out there, you would be correct).
Further, let's assume that there is no urgency for the jobs sent to the Photo Printer, and that the Text Printer needs to be more readily available. Your pictures can print in the dead of night for all you care, but you don't want to wait several minutes for photos to print when you need to print a letter or an invoice and go on to the next task.
In this scenario, it would be useful to schedule the Photo Printer so that the print device is not tied up while you are waiting for the Text Printer to get that invoice printed so you can get it out the door before the mail pickup. You therefore need to restrict availability for the Photo Printer. Here's how: