Evidence suggesting that low inflation promotes growth has motivated recent decisions by a number of central banks and governments, most notably New Zealand. Canada, the United Kingdom and Sweden also have moved in recent years to establish monetary policy with official low inflation targets. Decisions to adopt a policy objective of low inflation suggest that other policy-makers are reading the evidence pertaining to inflation and growth as we are. Consistent attempts to expand the economy beyond its potential for production will result in higher and higher inflation, while ultimately failing to produce lower average unemployment. Therefore, most economists would argue that there are no long-term gains from consistently pursuing expansionary policies.
Monetary policy can determine the economy's average rate of inflation in the long run.
And that's important for the economy, because high inflation can hinder economic growth. For example, when inflation is high, it also tends to vary a lot, and that makes people uncertain about what inflation will be in the future. High inflation also hinders economic growth in other ways. For example, because the tax system isn't in agreement with inflation, high inflation arbitrarily helps and hurts different sectors of the economy. In addition, it makes people spend their time hedging against inflation instead of pursuing more productive activities.