One reason, By increasing your deductions and expenses it will decease your income and you may not be getting as many credits as before like the EIC credit. You can't go by the refund monitor until you have entered everything in. Also after you reduce your income to zero there is no more refund to get back. But even though your taxable income goes down and you owe less income tax on it, you still owe SE Self Employment tax if you have a Net Profit.
You may have tax credits which are based upon earned income, so when you enter your expenses in the business, your income drops and the tax credits drop, as well. Common tax credits which are based on earned income are the Child Tax Credit and the Earned Income Credit.
If this is the case and you have purchased assets for your business, such as a computers or tools, which are more than $200 each and will last for more than one year, you may be able to spread out the cost over multiple years and reduce your expenses for this year. Check for the Expenses section in your Schedule C and then Assets.