A tax credit is generally more valuable than a tax deduction or tax allowance of the same magnitude because a tax credit reduces tax directly, while a deduction or allowance only reduces taxable income and so the reduction in tax is only a fraction (the marginal tax rate) of the deduction or allowance.
In the United States corporate tax payers may lower the total amount of tax they owe to the federal government, via programs such as the New Markets Tax Credit Program.