Let's look at AUD. Good primer of so called "resource currency".

For such currency exchange rate is used to redistribute wealth from society to the resource exporters.
As AUD drops, resource companies get more AUD for same amount of resources sold, and all else from Australia can just buy less goods in world market.

So, why elites need exchange rates adjustment? This one is easy. Resource companies are financed by banks, government stimulus and such course changes. As AUD drops company income in AUD rises and it can hire more people or spend more for resources development. Paradoxically, in current market it happens in situation of resources shortage. As resources prices are tightly controlled in world markets (to prevent instability), exchange rates are soft method to make people of specific country pay for resource development projects.