The IRS generally rejects most penalty abatement requests, however if there were certain conditions beyond your control which barred you from paying your taxes, the IRS may remove interest and penalties on your tax debt and allow you to only payoff the principle amount.
For example: Taxpayer was erroneously advised by his accountant and consequently IRS has accessed taxes and penalties due to the bad advice. A tax attorney can negotiate with the IRS in removing penalties, interest associated with such penalties, and reduce your tax debt.