No harm comes to dogs by eating grass. Dogs eat grass for various reasons: some do it to calm an upset stomach, others to provide bulk to their diets and some probably because they just like its taste.
If your dog has no signs of illness and has a proper nutrition, then eating grass is no reason for concern. However, you should check if the grass that he eats is being treated with herbicides, insecticides or fertilizers that can be toxic to the dog. If the dog eats the grass of your yard, then you can minimize this habit by having the grass cut short.
