 They also influence choices about working, saving, and investing, and affect the distribution of income.The amount of reduced federal revenues are significant, estimated by CBO at nearly 8% GDP or about $1.5 trillion in 2017, for scale roughly half the revenue collected by the government and nearly three times as large as the budget deficit.Since eliminating a tax expenditure changes economic behavior, the amount of additional revenue that would be generated is somewhat less than the estimated size of the tax expenditure.