Cast iron is denser than other pan materials, making the pans unparalleled at retaining and evenly distributing heat, but also somewhat heavy. Therefore these pans are excellent for applications such as searing, or any time when a pan must stay hot even as ingredients are added.
The pan retains its heat better than most other materials. They can also be put under a very hot broiler or into a barbecue or campfire — something that would completely destroy a non-stick pan, as they are all-metal and would have to be melted to suffer damage. Contrary to popular belief, acidic foods can be cooked in cast iron, provided they are removed from the pan as soon as cooking is complete.
Cast iron pans can be used for other kinds of cooking as well, although their heaviness makes them somewhat awkward for making, say, crepes, or any other kind of cooking where the pan needs to be moved around a lot during cooking. Cast iron is also less conductive than other materials such as aluminum and copper. This results in the aforementioned excellent heat retention, but also means that cast iron cookware takes longer to heat up and cool down.
Cast iron needs to be seasoned to provide a more-or-less non-stick surface. This process involves heating oil so that it polymerizes and binds to the pan. This creates a non-stick surface chemically similar to a plastic coating. Some people see this need for seasoning as a drawback; however, because the seasoning can be removed (with steel wool, even!) and reapplied as needed, cast iron pans can be maintained in excellent condition far beyond the life of a typical non-stick pan.
Properly cared for, a cast iron pan can last for generations. Thus they are an excellent value: extremely durable, costing less than all but the cheapest non-stick pans, while outperforming all but the most expensive cookware. The main drawback is that they will rust if washed in a dishwasher or left soaking in water. Also, they should not be washed with harsh, lye-based soap, as this will remove the seasoning.
They can be effectively cleaned with a stiff brush, plastic wool, or by rubbing with a paper towel, vegetable oil, and any salt, used as a mild abrasive. Prior to putting them back in storage, if you heat them up, empty, for few minutes, any remaining dampness will evaporate. Generally these retail for no more than US $20.