By default, Turbotax uses your standard deduction from the very beginning, so you have the benefit of that even before you go to the deductions area. If you do not enter itemized deductions that add up to be more than your standard deduction, then when you finish the deductions section, Turbotax tells you to use the standard deduction. You don't see any change because it had been in your return from the very beginning.
The standard deduction reduces only ordinary income tax. Neither standard or itemized deductions reduce self-employment tax on net self-employment income or penalties for early withdrawal, or penalties for not having insurance.
