The different bacteria, along with less effective digestion, mean smellier diapers. Even their skin and breath smell different. Breastfed babies are more portable. A nursing mother never lacks for the right food at the right temperature in the right amount at the right time - anywhere. Without bottles and pacifiers, nursing babies are simpler to carry along.
Breastfed babies are healthier.
Formula gives no protection against illness, so formula-fed babies are more prone to diarrhea, ear and respiratory infections, skin problems, and pneumonia. Formula-fed babies tend to get sick more often and recover more slowly than normal. And sick babies are not much fun. Formula affects longterm health, too. How a person was fed as a baby affects his or her risk of childhood diabetes, childhood cancer, ulcerative colitis, obesity, and perhaps heart disease.