Unglazed earthenware pots were for some time the only type available. These allow water to evaporate through the sides, and also allow air to reach the roots, discouraging rot, a particular advantage for moisture sensitive species. Roots can however be damaged by cold due to evaporation.
Glazed earthenware and plastic pots prevent evaporation through the sides. This means they need less watering, but increase the risk of roots being damaged by excess moisture. Plastic pots can also get very hot in the sun and cause roots to be burnt.