An uncoated cast iron pan can give a metallic taste to your food, especially if the coating has worn down. This happens when you cook a lot of acidic foods in the pan. Thus, it is better if you avoid cooking acidic foods like simmering tomatoes for making sauce. Since the cast iron gets extremely hot, we suggest you to avoid cooking delicate dishes like fish as it can break apart easily. Also, until your pan is seasoned properly, it will be better if you avoid cooking sticky foods like eggs.