Biologically, it has nerve endings which are sensitive. These nerve endings help enhance the mother-infant bond by ensuring a good latch. The fact that there are other uses for the breast is not really germane to breastfeeding. An apt, if unpleasant, comparison is that most normal men do not derive sexual pleasure from urination, despite the fact that they are using a sexual organ. In fact, you may be surprised to know that statistically, breastfeeding mothers have been shown to sexually abuse their children less often.
Experts say that the deepened bond between many mothers and their nurslings makes abuse less likely.
Breastfed toddlers may be more secure, perhaps because they have come to rely on their mothers as a solid source of comfort, and know that mother can be depended on when needed. Breastfeeding will delay fertility, and for some women, decrease their libido. The good news is that fertility will return for most women despite nursing a two or three year old. The fertility reducing affect of breastfeeding varies from woman to woman. The idea of nursing an older baby makes me uncomfortable.