If there's paper left over from a printing job, you've wasted money. That's why it's important to keep paper size in mind.
Most printers use a sheet of paper that is either 23 by 35 inches or 25 by 38 inches. Sometimes you can save money by having two or three jobs printed at the same time on the same sheet. Many times there's enough room left over to print a business reply card, a routing slip, or a bill stuffer. The extra job should cost you very little because you've already paid for the paper and press time.