Population of the planet Earth is growing and feeding all those people needs more and more space. We can't do that effectively with current technologies. Agriculture consumes big part of all our water and other resources and this situation is unsustainable.
One of the solutions is to move places for food production closer to consumers. It can not only eliminate the need for transportation, but can also connect needs of housing and production to create an effective system for inhabitants' life.
However, dense city centers require different approach to farming. The land needs to be used more efficiently, so it should be stacked to have smaller footprint. Farming inside of buildings, in controlled conditions, leads to bigger harvests.
Meaningful use of water (rainwater and water used in the production) in nearly closed system can save up to 99% of our current water consumption.
Waste from planting and residential can serve as an energy source and can lead to self-sustainable buildings.
Adding planting spaces into dense city centers or business districts can also serve as vertical parks and bring new places for inhabitants' recreation and education.