Changing your withholding has no effect on the tax you ultimately owe, it only changes whether you owe or get a refund.
The tax you ultimately owe (your tax liability) is calculated on your tax return. If you have less withholding than you owe, you will have to make a payment when you file. If you owe more than $1000, the IRS can assess an underpayment penalty with interest, because you are supposed to pay as you go. If you have too much withheld, you get the excess back as a refund.
