More technically, as long as prices are fairly stable, changing a nominal variable such as interest rates can temporarily affect real variables, including quantities of goods and services. This is useful when demand is too weak, during downswing phases of business cycles.
Where a central bank aims for a growth rate which requires more output than an economy can produce, however, the results are troublesome. For a small open economy such as South Africa, this typically means that we experience unsustainable imports, currency depreciation and rising inflation.