Unless you want to wait FOREVER it is worth it to pay a little more. At least FedEX or UPS care that your letter or package actually gets delivered!
I'm in the midst of some heavy-duty carton shipping. UPS STORES (franchises) are outrageous in their charges. The UPS warehouse/shipping center was slightly lower in cost than the STORES. I'm now using the U.S. Postal Service exclusively and it's saving me a considerable amount of money.
USPS delivery time is generally one or two days later than UPS. Makes no difference to me. If someone needs express service when shipping Grandma's cheesecake, this service is available with all delivery companies, including the Post Office.
A one-hundred-percent-perfect delivery system does not exist on this earth. Even the divine love arrows shot by the Roman god, Cupid, oft miss their mark.
Leni