Clog...clog...clog...
Brandon, Evan is correct in what he says. A vacuum cleaner dustbag is not just there to hold the dirt; it acts as a filter, which separates the dirt from the airstream, as the dust particles get caught in the pourous bag's surface area. As you continue to vacuum, more and more of the bag's surface area gets clogged with dirt particles, which stifle the airflow through the machine, and reduce it's performance. This is demonstrable, scientific fact. Dyson have drawn the public's attention to the problem, and used it to their great advantage. Awareness of the problem is nothing new, though; in 1916, Hoover were printing in their manuals:
'The bag should be emptied frequently, because a dirty bag will reduce the efficiency of the sweeper.'
In 1919, they wrote,'Empty the bag after each cleaning, as a dirty bag holds in the air, and retards the machine in it's cleaning.'
In Model 305's manual, they went even futher:
'Empty the bag after every cleaning. All cleaners are most efficient when the dirt bags are clean. As the bag collects the dirt, the flow of air through it is decreased and a pressure is developed which reduces the effiency of the cleaner.'
So you see, it's not just something Dyson made up!
HOWEVER, to what extent the clogging reduces cleaning performance in vacuums is a hotly debated topic! For instance, 'Which? Magazine', the UK equivalent of Consumer Report, noted in April 2007, ‘Our tests have found no link between the presence or absence of a bag, and cleaning ability.’ I'm sure people here will queue up to tell you how many cleaners, vintage and modern, will give perfectly acceptable performance with a half-full bag, which I would agree with in many (not all!) cases.
I have no preference between bagged or bagless cleaners. What I like about bags is their simple, neat, tidy and clean nature of dust-disposal. What I don't like about them is the cost - really decent ones, such as Miele's, are pretty darn expensive for something you're ultimately going to end up binning! What I like about Dyson is that it is simple, and relatively clean compared to other brands, to dump the dirt in the outside bin, click the canister back into place and keep going. To me, that's the real advantage of bagless cleaners, not the whole clogging issue....
