Around the middle of the first year solids may be introduced, but breastmilk should continue to be the main source of nourishment during the first year of life. If your baby gets sick, the breast is capable of producing antibodies and providing them to the baby. If mother or baby gets sick, there's rarely a need to interrupt breastfeeding. Breastmilk protects baby from infections and gastrointestinal problems. This translates into fewer trips to the doctor.
Breastfed babies travel very easily.
No need to worry about figuring how long you'll be gone and how many bottles you'll need - warm milk is always available. Not only does breastfeeding help space babies, but by not having monthly cycles, a woman's body is able to have that time to recover from childbirth and avoids having the loss of blood during menstruation. For more information on how to space your babies naturally, a good resource is Breastfeeding and Natural Child Spacing by Sheila Kippley. Most formulas are based on cow's milk, which is made for a calf. Because of its high protein content, cows milk must first be watered down.