Power Units - Bagged vs Bagless
There are two typtes of Ducted Vacuum Power Units - bagged and baggless.
Bagged Power Units use paper or cloth bags to filter and collect the dust, whilst bagless ducted vacuums use cyclonic filtration to filter and store the dust in a dirt collectors.
The benefit of a bagged Power Unit is that they are a simple drum with a bag inside. It is very quick and easy to remove the bag and then dispose of it. It is imperative that the bags are replaced when the dirt level is nearing the the top of the bag otherwise the efficiency of the vacuum (mainly the suction) may suffer.
A bagless Power Unit will give the same or similar performance as your bagged ducted vacuum system. Instead of using a bag, bagless systems use cartridge or foam to filter dust. The advantage is obviously you won't need to buy bags to run the system, the disadvantage is the unit may need regular maintenance, ie the filter has to be cleaned to keep the suction level high, because dust stuck in the filter will reduce the airflow and also the vacuum power.
Apart from one using bags and the other using a dirt canister, both Power Units, remove all vacuumed dust, dirt and allergens out or your living area and into a canister - usually located in the garage - to dramatically improve indoor air quality. That makes for a healthier home even if you don't suffer from allergies.