Salt is used in ice cream makers to help lower the melting point of the ice that is packed around the base of an ice cream maker. A lower melting point allows the base of the machine to cool enough to freeze the ice cream.
Fat and sugar in the mix used to make ice cream keeps ice crystals from forming easily, causing it to freeze at a lower temperature than plain water. Without the addition of salt, the ice would melt before it completely freezes the ice cream in the maker. Ice cream does not freeze until it reaches a temperature of 27 degrees Fahrenheit.