The industrialist Andrew Carnegie used his vast fortune to build 2,509 libraries around the world. The people of Little Free Library would like to continue that philanthropic tradition and make it accessible for people without Carnegie's wealth. So they sell birdhouse-sized libraries that you can fill with books that people in your neighborhood can read.
Link -via Super Punch
I think this would be especially beneficial in smaller towns where a regular library is not easily accessible. Additionally, why not offer this in areas where older people live that perhaps cannot get to library so easily. Country Inns & Suites, the hotel chain, has a similar program. They offer books in their lobby for their patrons to borrow and they can either return it to the hotel they took it from or just drop it off at another hotel in the chain. They've offered this program for many years and since it is still going there must be a benefit to it.
Admin moved it out to a hallway, then the books vanished. A few people left money, and that vanished too. I was pretty disappointed in everyone.