Family planning is the combination of activities that allow couples to decide on the number and spacing of their children. There are several reasons why family planning is important for society at large.
For example, having the choice of waiting before having children allows young couples to have more established careers and be in a better economic position by the time the children arrive. This means they will be better equipped to raise functioning members of society, and to provide for them adequately.
Also, giving enough time for the mother to recover can allow her to take better care of the baby and of herself. The baby can grow up healthier and the mother can take part in society more fully.
Finally, overpopulation is a serious problem in many places all over the world. Family planning might lead some couples to have less children, or not at all, reducing the burden on society and contributing to alleviate the problems of overpopulation.