The government might enact expansionary spending when it is trying to stimulate the economy.
Public spending or its decrease is an economic policy instrument called fiscal policy.
Fiscal policy can be contractionary, when the government wants to cool economic activity by reducing public spending, or expansionist, when the government aims to stimulate the economy by increasing public spending.
When the government increases its spending in a given sector, it stimulates the productive chain of that sector, boosting economic activity and consequently affecting GDP. For this reason, public spending is usually strategic. For example, spending in the infrastructure sector boosts the production of the steel and cement industry and their respective production chains.
In addition, the government can increase its social spending, that is, by injecting money into the economy through transfers and social programs. In this way, people consume more, which stimulates aggregate demand, also affecting GDP.
Therefore, the increase in spending is an expansionary fiscal policy aimed at stimulating the economy.
