A modestly positive inflation rate also reduces the probability that the economy could fall into deflation, which under some circumstances can lead to significant economic problems. Although attaining the long-run sustainable rate of unemployment and achieving the mandate-consistent rate of inflation are both key objectives of monetary policy, the two objectives are somewhat different in nature.
Most importantly, whereas monetary policymakers clearly have the ability to determine the inflation rate in the long run, they have little or no control over the longer-run sustainable unemployment rate, which is primarily determined by demographic and structural factors, not by monetary policy.