I am not sure what you mean, but I'll lay out how it works...
You do not have to use your HSA to pay for qualified medical expenses, but the option is always there. Using the HSA to cover medical expenses is generally better than trying to use Schedule A, because you can deduct on Schedule A only those medical expenses in excess of 7.5% of your adjust gross income (AGI), but you can use HSA funds to pay for any medical expense that is not reimbursed by insurance.
One thing is that if you report a distribution from your HSA by entering your 1099-SA, TurboTax is going to automatically subtract that amount from the medical and dental expenses reported on Schedule A. Why? Because TurboTax assumes that you entered all medical bills, and then TurboTax asks you for insurance reimbursements which it subtracts from the bills and does the same with HSA distributions.
This is a problem for those taxpayers who entered only their net medical bills, i.e., the bill minus any discounts and insurance reimbursements. Their medical and dental expenses are artificially reduced in this case.
The solution for a taxpayer who both (1) had HSA distributions and (2) wants to also try to deduct medical and dental expenses on Schedule A, is to add a miscellaneous item at the end of the Medical interview that has the description of "HSA paid expenses" and the amount of the HSA distribution (from the 1099-SA).
In this way, the HSA distribution is subtracted from the miscellaneous entry, and the result is that your medical and dental expenses are not artificially reduced.
