" the great force with which air will pass through the filter. And it eliminates a space-consuming appliance and an additional sound in your home. On the other hand, the filters may be more expensive and more difficult to handle; and they may need to be changed more often. Consult your doctor and your heating service on this alternative to a portable system. Applying the already-existing fan"
They also provide the added benefits of keeping your expensive heating/cooling system cleaner and running more efficiently.
Back to the HEALTH benefit – it’s totally true that the jury is still out on that as it relates to air cleaners. It’s also totally true that high efficiency air cleaners installed in your HVAC system capture alot more crap than any portable device or regular furnace filter. Just look at a dirty filter coming out of one some time. All that crap is airborne before it’s trapped in the filter.
It’s also totally true that I know allergy sufferers who swear by them.