Here's part of the article I was reading
For a prime cut you can take it off as soon as it reaches the target temp, although a prime cut will also benefit from extended time at the target temperature. For Secondary cuts, it is essential, the "time at temperature" secret is what does all the work! The secondary (hard working) cuts (generally from the front of the animal) are loaded with connective tissue. Connective tissue is primarily made of collagen, which is tough and difficult to chew. The good news is, collagen is broken down by the long term application of heat. Luckily for us, collagen breaks down into unctuous and delicious gelatine, giving what was a tough cut new life!
This magic of the Collagen breaking down starts when the meat reaches 55-60°C (130-140°F), but at that temperature will take a minimum of 48hours to work its magic on a Brisket. In a Sous Vide water bath, this is no problem, but difficult to do in a BBQ or Smoker.
So in BBQ we take advantage of the fact that the Collagen conversion is most rapid at temperatures over 82°C (180°F) internally. It is common for a cooking Brisket to “Stall” at 65 to 70° C (149 to 158° F); this is thought to be because of the massive amount of energy needed to convert Collagen to Gelatine and surface cooling from the meat “sweating”.
Old school BBQ philosophy had us cooking at a dead even temperature, commonly 120-135°C (250-275°F) for 10 or 12 hours until fork tender and roughly 95° C (203° F) internal temperature. Some of the newer theories increase the temperature and shorten the time, but there is no escaping the “Time at Temperature” reality!
Now remember that every piece of meat contains Collagen, not necessarily in thick visible wads but as the wrapper that holds the meat strands into bundles within the muscle. So it follows that the longer you can hold at temperature, the more of the collagen holding the meat together will dissolve and the softer or more tender the meat will become.
This is the secret of Sous Vide and the new frontier of BBQ.