Here's what she says: USPS flat rate boxes are very convenient. But, they aren't always the best deal. If you are sending items that don't weigh much, such as clothes, and you aren't sending them to Alaska, it's probably less expensive to put them in a regular box and send them. But, if you are sending books or a mortar and pestle, or jars of homemade jam, flat rate boxes are a great savings. And, USPS will give you $2.00 of a large flat rate box sent to anyone with a military address.
Make sense right? I also didn't know about the $2 discount for large flat rate boxes if you are sending to a military address. Thanks for the money saving info!