The thing that is most important about the growth rates of many less economically developed countries is the fact that they tend to be very high. Poorer countries tend to have much higher birth rates than richer countries and therefore tend to have populations that are growing relatively quickly.
In poor countries, the birth rates tend to be very high. There is relatively little use of contraceptives in these countries. Even though medical care in such countries is relatively poor, it is good enough to keep death rates low enough to allow populations to grow rapidly.
This is important because it helps to lead to some problems for these countries. These countries have more difficulty providing for their growing populations. Their populations are growing faster than their ability to provide for them. This means that a high rate of population growth leads to economic and social problems in these less developed countries.