Some have argued that discretionary monetary policy has created more problems over the last 20 years than benefits. The alternative is to have a relatively strict rule that allows the money supply to grow based on things like the growth rate in the overall economy. The anticipated benefits of supply-side policy are faster rates of economic growth and limited inflation. AS curve will shift outward if business taxes are reduced, if taxes are cut on business investment, if regulatory costs are reduced, such as through deregulation, if education is enhanced to increase the value of human capital, of government invests in needed infrastructure such as roads, ports, and technological infrastructure, and if welfare policies are hardened to promote a larger labor force. Thus it may be impossible to coordinate macro policy, or to fashion any perfect policy to moderate the business cycle.
Forecasting is very difficult.
If we wait until we know for sure, then we miss the opportunity to really avoid the problem to begin with. Cut capital gains taxes to the rich, or cut income taxes to the middle class. The time between emergence of a problem and policy response to a problem may become more than a year, particularly for fiscal policy, and these policy lags may largely or even totally eliminate the effectiveness of macro policy.