Paid state taxes from previous years in 2017

I paid state taxes from previous years in 2017.  I followed the instructions to claim this under "prior year state or local tax payments".  It was the last thing I filled out in turbo tax and it did not change anything on my federal tax refund.  My federal tax refund stayed the same.  It did reduce how much I owed to my state.  Can anyone tell me why that is?