The Aswan high dam was built between 1960 and 1972. It has two primary functions: to control the level of the river Nile, and to generate electricity.
Only 4% of the land in Egypt is cultivated; essentially that is the narrow strip alongside the Nile. Every year this land was flooded, together with almost every one of Egypt's towns and cities (there are no significant towns or cities apart from those either beside the Nile or beside the sea).
Since the building of the dam, this flooding no longer takes place. In the distant past the floods were essential to life as they provided silt and irrigation; modern methods can substitute these features so that stable year-round farming is possible, and the cities no longer flood as they did every year.
The dam provides 70% of the nation's electricity, and even enables Egypt to export electricity to its neighbours.
The disadvantages were that Lake Nasser displaced almost the entire Nubian race from their lands, and that a number of ancient temples had to be rescued from the rising waters.
Nasser was the first Egyptian ruler since the Pharoahs (after invasion by the Greeks, the Romans, the Turks, the French, and the English). The ancient rulers built pyramids to be lasting monuments; the High Dam could be considered as Nasser's pyramid.