Unfortunately for people who don’t like to think too much about their food when they’re done cooking; leaving your food in a cast iron pan overnight is not a good idea. Now, as long as the food is processed, not too perishable, and refrigerated — there won’t be any issues with the food itself. However, you’ll find that this sort of practice severely diminishes the effectiveness and preservation of your actual cooking pan. As you might have realized by now, cast iron is not a material that’s as treated as some other industrial polymers for cookware. Consequently, you have to work harder to preserve it. For instance, after you season and dry it; you don’t want to allow any moisture to gather as it can damage the pan. And that’s especially true for moisture from leftover food, because it may be acidic and eat away at the seasoning. Lastly, there’s a slight metallic flavor that the food might develop if it’s in the pan for too long.