Overall, population centers are more economically productive. You have more people collected in a smaller space, so workers and industries can cooperate more effectively. Countries' levels of urbanization have and, to varying degrees, continue to have a strong correlation with their level of wealth. You have more goods and services available within a smaller area. Workers have more job opportunities.
Urbanization also has good environmental effects. It makes cleaner modes of transport, like trains and subways, much more feasible. Power and water has to travel a smaller distance (except for when people put cities in dumb locations with regards to water distribution, like LA). Dense countries tend to have a smaller carbon footprint compared to more rural countries with the same standards of living.
Basically, there's a lot to be gained by populations shifting from rural areas to the city. I'm not so sure why many are so eager to lament a shrinking rural population.