In normal times, this so-called “separation principle” allows the central bank to fine-tune operational procedures in order to steer shortterm interest rates very close to the main policy rate, without risking that those adjustments are regarded by observers as changes to the monetary policy stance.
In exceptional circumstances, when severe distortions in financial markets emerge (reflected, for instance, in volatile and rising money market spreads), a more non-standard liquidity management by the central bank may be needed without jeopardising the central bank’s main monetary policy objective.