It depends on how dirty the carpet is and whether there is anything entangled on the carpet. However, about seven passes should do it for a really dirty carpet. If you clean regularly or the carpet is not very dirty a couple of passes will do it.
When comparing between bag-less and bagged vacuum cleaners, there isn't a clear winner. The choice here depends on the needs you have since each model has its own advantages. The bagless models save on costs of purchasing disposable bags. The plastic bins on the bagless models are small and need to be emptied and cleaned often. For the bagged models, you only need to detach the bag when full and dispose of. The bags are big and do not need to be emptied often. Go with the vacuum cleaner that suits your needs.
As the vacuum cleaner ages, it is possible to note some reduction in suction pressure. This could be because of lack of maintenance or a faulty motor. When the motor is faulty, the fan doesn't rotate as required which consequently means that the suction pressure reduces. It can also be because of;
buildup of dirt and grime on the air filter.
Blockage of the air hose
Air leakage through an opening or damage to the vacuum cleaner
Yes. You can clean hardwood floors using a vacuum cleaner. It is actually a recommended method it does not wet the floor or scratches.