This is what I am saying, a country that can make its population efficient, that population will become the wealth of that country. India is currently trying its best to utilize its population properly and they have been quite successful. To keep a country in balance, youth is needed for which the birth rate is an important factor, if the birth rate of a developed country continues to decrease regularly, then at some point the number of old people in that country will increase and the working youth will decrease. So population and birth rate are very important in determining the future of a country.
There are developed countries (like Germany and Japan) where birth rate is very low and government is trying to increase birth rate by giving incentives to families. Skilled labor from developing countries find such countries ideal place for immigration. Birth rate is a real issue specially in developing countries of south Asia and Africa. The government can only afford a certain level of population based on its available resources.