Advantages for whom ? Generally, in a smaller family the resources are distributed among fewer people, which means that the children can get a better education and more support and the parents don't need to work us much (e.g. double shifts) to support their family. For the whole state, a 2+2 model is also the most sustainable, where there are no drastic differences in population age over time:the number of people stays constant if everyone has around 2 children.