Used with Mylar, these remove the oxygen that causes fats to go rancid and insect eggs to hatch. That is a real extension on grains, oats and flour, which go off through oxidation long before they go off microbiologically.
One caution worth stating plainly, because the prepping corner of the internet is careless about it: removing oxygen creates an anaerobic environment, and for one organism that is help rather than hindrance. The vacuum-packing page covers why this is fine for dry goods and emphatically not a way to store anything moist.