What’s the purpose of deferred deportation?

For discussion:

Here’s a recent New York Times article on illegal immigrants with deportation orders that, for various reasons, the government has not actually acted on.  The Times lists a number of circumstances:  the individual officially “low priority” or was given a deferral (e.g., a sick child), or the deportation order was issued in the individual’s absence (and that due either to willful refusal to cooperate, or because they had moved or didn’t understand the English-language notice).

But here’s the question:

Should an individual with a standing deportation order consider it a “true” order, with a delay that permits them to get their affairs in order, or should they consider the deferral as equivalent to a government decision not to deport, that is, permission to remain in the country indefinitely?  And, given that the government can choose to act on pre-existing deportation orders at any time, is it an injustice to do so, or have people in this situation been given fair warning, due to the fact that — duh! — they have been issued a deportation order?

Image:  https://commons.wikimedia.org/wiki/File%3A100203houston_lg.jpg; By U.S. Immigration and Customs Enforcement (ICE), www.ice.gov. Please credit by saying “Photo Courtesy of ICE”. [Public domain], via Wikimedia Commons