Answer: To prove your income and expenses

When you use tax preparation software, you need to enter your income and expenses from the previous year. This information is used to calculate your tax liability.

The W-2 and 1099 forms are used to verify your income and expenses.

The W-2 form is issued by your employer and shows how much money you earned in the previous year. The 1099 form is issued by businesses and individuals that have paid you money for your services.

Without a W-2 or 1099 form, the IRS will not be able to verify your income and expenses. This could lead to an audit or a tax penalty.