Sometimes there is not enough of the official currency to facilitate a healthy local economy. We swap our goods or our labor for something else of value. Money was invented for this purpose, but when there is a shortage of that commodity, true creativity comes up with another way.
Direct swaps are sort of hit and miss.
A LETS allows the parties to agree on the value, make the exchange, and record the transaction with a locally credible network. Bernie grows corn and sweet peas for her family in the back yard, but this summer has an excess. Bernie's daughter would like to learn piano, but the money is needed for bills. Cary works on cars and business is a little slow right now, but he loves fresh vegetables. A LETS facilitates everyone's efforts and needs.