Traditional IRA contributions are an above-the-line deduction and may directly reduce your reported wages, reducing your taxable income. For some incomes, this might allow you to qualify for other deductions and credits due to a lower adjusted gross income (AGI).
If you (or your spouse, if filing a joint tax return) are covered by an employer-sponsored retirement plan, there's a phase-out range. Depending on your income, you may only deduct part or even none of the IRA contribution.
Roth IRA contributions aren't deductible.