I don't send letters by post but I often need to send packages by post. Perhaps it's returning some merchandise where the merchant didn't have free shipping. Perhaps it's shipping a security key to a close friend so I can have offsite backup of a key. When I moved, I got rid of my book collection by asking friends which books they wanted and I shipped it to them (media mail is cheap).

It's efficient to transmit information over the internet, but it's still essential to send physical items by post. When I visit USPS branches, I always see plenty of people mailing packages.