Lets start with India, which is one of the strongest economy nations, but they simply have too much population to handle. So if little bit Indians migrate to other countries it might help them. Population effects economy a lot. Overfilled countries can help less populated countries. Migration will maintain balance through out the world. But big question is that whether if it ever going to happen.
Mass migration can provide economic opportunities for people who cannot find work in their home country. Skilled workers can find job openings in countries where there are not enough workers with the proper training or skill set to handle the work. It is often detrimental to the workers' poorer-performing home country, though, since it leads to a brain drain (or talent drain). An employed immigrant population also raises a country's GDP.