Flat rate priority mail is designed to make the shipping process convenient for customers. The United States Postal Service provides the necessary mailing supplies and a constant cost regardless of how far the package is going to allow for easier budgeting. Whether that represents a good deal or a poor one depends on how much the item being mailed weighs and how far it's going.
Weight and Distance
Any package that weighs up to 70 pounds and fits into a designated flat rate priority mail envelope, box or tube can be sent via flat rate priority mail. Everything else is priced based on weight and the number of zones traveled. Zones range from 1 to 8, with Zone 1 being the closest to your location and Zone 8 the farthest away. A lightweight envelope or package delivered locally will be cheaper to deliver using standard priority mail instead of the flat rate service, while heavier packages going longer distances will be cheaper to send via flat rate priority mail. The postal service provides a pricing calculator on its website that allows you to plug in the specifics of your item to see which option is best for you.