Originally grain free foods were offered to provide some relief to dogs that had allergies to common grains like corn, wheat or soy. They did work well in those situations. Now it is like many dog food traits it has become a marketing tool and fad to offer or use grain free products. The manufacturers created the feeling that grain free is better for everyone. Nutritionally I have no problem with dogs eating diets containing well designed amounts and types of grain. There are many valuable nutrients in grains. Using these diets to help manage allergies in adult dogs can work well but I do not see any advantage for young, growing dogs.