This is my summary  about Bagged Versus Bagless For Vacuum Cleaners :

1.Whether you have a bagless HEPA filter, a pre-filter,
or disposable bags, they all need to be changed at
some point. With the average life of a Vacuum
Cleaners, you can expect to spend the same on either
collection system for filters, but if you value your
time, you can expect to spend quite a bit more on
a bagless system

2.With bagged vacuum cleaners, the performance will
start at 100% with each new bag then slowly drop
as the bag starts to fill. Just how quickly the
performance drops depends on how well the bag is
constructed. With the average Vacuum Cleaners and the average
bag, you may replace the bag every 3 - 4 weeks
with 90% of performance the first week, 70% in
weeks 2 and 3, then 50% of less in the fourth week.

Ok,this is only my summary about Bagged Versus Bagless For Vacuum Cleaners.For full story,visit Vacum Cleaner info center site here : http://thevacuumcleaners.blogspot.com/