The claim was that pollutants would go through the vacuum and out the exhaust, distributing them back into the air, where you then breathe them in. It was better to just let them sit. While this argument made sense, it struck me as primarily being a critique of a poorly designed tool: I vacuum to remove unwanted matter from my living space, not to redistribute it within the space. So I did the obvious thing and bought a Miele vacuum with HEPA exhaust filter from the Germans. For the past four years my vacuum has been effectively the same as my air filter. I can use it regardless of environmental conditions, even during the 36-hour night.