The postal service is a good example of a government function that provides some services that cannot be made efficient.
My dad lives part-time in an unincorporated village in Alaska which has a population of 13 as of the 2010 census. Once a week, the USPS essentially charters an airplane to deliver mail there, for which senders pay the same rate they would to send mail anywhere else. The postage obviously doesn't come anywhere near covering the cost of delivery. Without this subsidized mail delivery, which is often used for groceries and other supplies, the full-time population would likely drop to zero. While it's likely that at some point in the future, if that kind of mail service continues to exist, drones will make it more efficient, it will always be much less efficient than delivering mail to people who live in cities.
It's reasonable to ask whether it's desirable to continue to subsidize people choosing such a lifestyle, and there's a good argument to be made that it is not. Many of the people who live in remote parts of Alaska have a rugged individualist mentality and a dislike for the idea of subsidies, but tend to get quiet when theirs are mentioned.