One reason is that some income-based credits such as the earned income credit will decrease when you enter more expenses and decrease your taxable income.
Since we in the Community cannot see your tax return. You can look at your 1040 and Schedules 1, 2, and 3 to see what changes when more expenses are added.
Even on the Online product, you can see your 1040 and its schedules at any time by clicking on Tax Tools (on the left), then Tools (below it), then clicking on View my Summary (in the center), then clicking on Preview my 1040 (back on the left).
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