I believe I am on common ground in stating that from a theoretical perspective, the impact of fiscal policy on the economy is rather uncertain. Empirical evidence generally points to a positive but low impact of an expansionary policy on output. Therefore, the power of fiscal policy to reduce cyclical volatility or to stimulate the economy should not be overestimated.
Discretionary fiscal measures have proved to be ill-suited for fine-tuning the economy in the past. Due to time-lags it has often lead to a pro-cyclical impact on the economy. Moreover, asymmetric behaviour in recessions and booms has contributed to deteriorating public finances in the last decades.