It doesn't, really. A society that plateaus at a high standard of living is a very good end result.

However, the world isn't equal, nor is the wealth equally distributed. If all of the rich, developed world was to slow down and become stagnant like Japan, where will the demand for goods and commodities made by the developing world come from?

Huge western demand helped lift hundreds of millions in China and India out of poverty, for instance.

Stagnant growth might be good for an individual country, but it can doom developing countries to similar stagnancy.