Perhaps you filed your returns but weren't in a financial position to pay what was owed. You may have planed to catch up the next year, but now find yourself several years in arrears with a notice from the IRS, stating that you owe three or four times the original amount.
Tax penalties and interest can add up very quickly, and you may now be faced with a choice: you can write a check to pay the full amount, including interest and penalties. Or you can just keep ignoring notices while the penalties and interest continue to accrue.
