Clay, unlike other cookware materials like steel, iron or aluminum, takes a long time to absorb heat. But once it does, it spreads that heat evenly throughout the clay pot body and releases it slowly, to the food cooking within. This REALLY slow cooking allows for the flavors of a dish to build slowly, for spices to penetrate more deeply, and for meats, even the tough cuts, to break down into succulent pieces.
A second advantage comes from the unglazed nature of the clay pot. Because clay is in contact with the food as it cooks, the alkaline clay neutralizes the sour or bitter acids in foods like tomato or vinegar, mellowing it and making it taste a little sweeter. There are generations of anecdotal evidence to support this. Kerala, a southern state in India, is famous for its tamarind-based fish curry, a dish that is always cooked in an unglazed earthen pot, whether at a home or a restaurant. The secret, many say, of the famed fish curry is the magical alchemy of the clay pot itself.