The advantage is that a single child of love from the father and the mother, and not be Hee's father and mother, from love. His father and mother, saving costs and raising the child alone.
The advantage is that a single child is loved by both parents and are not subject to vie for the love of a father and mother. Parents cost of raising and caring for children alone.
The advantages are the only child love from both father and mother, and don't take love from father and mother. Father and mother, save costs, raised, attentive you alone.