So if you’re a serious Keynesian, you’re for maintaining and even increasing spending when the economy is depressed, even though revenue has plunged; but you’re for fiscal restraint when the economy is booming, even though revenue has increased.
Milton Friedman (1962):
When private expenditures decline for any reason, it is said, governmental expenditures should rise to keep total expenditures stable; conversely, when private expenditures rise, governmental expenditures should decline. Unfortunately, the balance wheel is unbalanced. Each recession, however minor, sends a shudder through politically sensitive legislators and administrators with their ever present fear that perhaps it is the harbinger of another 1929-33. They hasten to enact federal spending programs of one kind or another. Many of the programs do not in fact come into effect until after the recession has passed. Hence, insofar as they do affect total expenditures ... they tend to exacerbate the succeeding expansion rather than to mitigate the recession. The haste with which spending programs are approved is not matched by an equal haste to repeal them or to eliminate others when the recession is passed and expansion is under way. On the contrary, it is then argued that a "healthy" expansion must not be "jeopardized" by cuts in governmental expenditures. The chief harm done by the balance-wheel theory is therefore not that it has failed to offset recessions, which it has, and not that it has introduced an inflationary bias into governmental policy, which it has done too, but that it has continuously fostered an expansion in the range of governmental activities at the federal level and prevented a reduction in the burden of federal taxes. (Capitalism and Freedom, p. 76)