You can pay down tax debt, generally, without any further interest or penalty. This can be a substantial advantage. I have had many clients who have entered into Installment Agreements with the IRS but have not gotten anywhere with those agreements because the IRS is allowed to add a penalty of 11 percent per year, on top of the interest (which depends on the prime rate).
So, even in years where the prime rate is very, very low, e.g., 3 percent, you are still paying 14% per year on your tax debt. Imagine the cost of money when interest rates are more “normal,” such as 6-8 percent… the actual cost of paying back the IRS will mount to some 17-19 percent per year, basically an unsustainable payment in most cases, and one you should NOT do in most cases.