As a former tax accountant, the simple answer is never. You even have to file a final tax return after your death. Your estate may have to file a return depending on how it is set up. I did read the info that the link provided and do agree with the information.
I will tell you that many people that do not file returns because they "don't owe any tax" often miss out on tax credits. A recent example was the no worker left behind credit. Years ago during the Bush years each person was given a credit of ~$500/ person. Also, for those in the lower income area, earned income credit can be a surprising addition to your refund. Seniors are also beneficiaries of tax credits in many states. None of us like to pay taxes and certianly have high anxiety filing returns. However, you can benefit from doing so on occaison.
For those of you that want to save your money and not pay anyone, I have used H & R Block at Home (formerly Taxcut) since the late 1990s. I do not and have never worked for the above mentioned company. I used to use professional tax software and found this program to have similar results.
(a little known fact-April 15th is not always the federal tax filing deadline. (It is the 3rd Tuesday of April). In 2013 it will be April 16th. This year it was April 17th.