Fats for deep fat frying should be capable of being heated to a high temperature without smoking or burning.  Smoking impairs the flavor, the digestibility and the durability of the fat.  Once upon a time fat was used over and over for frying.  Over time the smoke became more so unless the cook cleaned the fat between frying.  We now know that this reuse of fat for frying can be dangerous to your health, so it is no longer recommended that you do it.