By respecting impossibility theorems we avoid wasting resources on projects bound to fail.
Sustainable growth is impossible.
Physically, the economy is an open subsystem of Earth's ecosystem, which is finite, nongrowing, and materially closed. As the economic subsystem grows, it incorporates an ever greater portion of the total ecosystem and must reach a limit at 100 percent, if not before. Therefore its growth is not sustainable. Economists will complain that growth in GNP is a mixture of quantitative and qualitative increase, not strictly subject to physical laws. They have a point.