I don't think there's any good or bad as they are dogs and in the wild they take what they can get, but as they have been bred certain dogs develop allergies the same as humans. Some people can live off rubbish and look pretty healthy and some can develop allergies or intolerance to certain foods (not taking into account long term effects) My other dog can eat anything and show no signs of anything yet the other two only need to eat a biscuit and they start scratching. If you're dog is happy and healthy on their food, stick to it, providing they are still getting the right nutrients to ensure a long term healthy outlook.