While not all states allow lenders to obtain a deficiency judgment, some still do as a way of obtaining maximum leverage against the borrower.
Also, since it is unlikely the lender will obtain the full amount of the debt from the foreclosure sale, the lender will seek to recover their full measure of damages against you in the form of a deficiency judgment.
This means if the lender sells the property for less then what is still owed on the promissory note, the lender can collect the amount of this deficiency from you as well.
To make matters worse, the lender may be entitled to court costs, interest and attorney fees related to the trial which gets added to the judgment amount you will become legally liable to pay. However, even after the sale of the property is made, in these states that permit a deficiency judgement, the homeowner still has the right of redemption.