There's a negative and positive effects, the negative is overpopulation. When there's an overpopulation crisis in a country it always affects the growth of that county as there's increase in crime rate due to so many individuals been out of school, job etc. When the government's of the nation doesn't have the wisdom to make use of the overpopulation to the benefits of the country it affects the country's overall performance and you can notice this happening in most third world countries.

The world is going digit and things can now be done with robots and devices that weren't possible in the past, we don't need overpopulation in the world anymore and the rate at which children are produced should be reduced by each family depending on their financial strength.