Some raw beans, for example kidney beans, contain harmful toxins (lectins) which need to be removed, usually by various methods of soaking and cooking. The soaking water from kidney beans should be discarded before boiling, and some authorities recommend changing the water during cooking as well. Cooking beans in a slow cooker, because of the lower temperatures often used, may not destroy toxins even though the beans do not smell or taste 'bad' (though this should not be a problem if the food reaches boiling and stays there for some time).
