This is just a recipe to spread weeds everywhere. If you mow them, most of the time you’ll just break them open and spread their seeds
Also if you mow your grass drastically shorter or you let it grow for a long time before mowing, do not fail to fertilize it from above right or soon after, start aggressively plucking the leaves of weeds (or other selective methods of fighting them) for a few weeks and (optimally, but highly recommended) verticulate it no sooner than 1 week after cutting. Also time it well to grant your lawn at least 3 weeks of ideal growing weather and climate (It won't die because of a week or two of awful weather, but you'll have A LOT more work fighting weeds ahead of yourself).