For a developing country, a growing economy, generally, means that people are better able to coordinate with each other and improve the quality of life (or in fact, are able to live above poverty lines). They are better able to help each other. And therefore, growing economy is often equated to being good. In a developing country, people should continually be becoming more efficient and productive (perhaps, by using technology). The population may be growing, and therefore to keep the per capita wealth same, economy should be growing.

That does not mean that making people more productive is the only way to increase economy. Economy can also be increased by simply increasing the production and consumption of goods. For example, if traffic increases, people will consume more fuel, but that does not mean people have become more productive. Such increase in goods' usage or activity of people may or may not be good for the society. (Example is an oil spill, that increased the GDP!) Wealth inequallity can also increase with increasing economy.

Thus, growing economy is, usually, a positive sign in developing countries. It need not be a positive sign, but it usually is.

References:

• Does the Economy Really Need to Keep Growing Quite So Much? - The Atlantic
• Do we need economic growth in a modern economy? - Economic help
• Why do we need economic growth? What would be so bad about keeping our economy the same size year to year? - Quora