In the beginning all vacuum cleaners were without a bag. All vacuum sweepers only used a cloth bag to contain the dust and filth. They leaked particles and odors, but they were much better than having nothing at all. Then paper bags were introduced to very dramatically cut down on the dirt. The paper liners were a great improvement because they cut down n the odors stored in the cloth outer paper filter bag, and the debris and dirt could be thrown away without a dirt cloud forming over the vacuum sweeper.
Approximately 1985 the without a bag vacuum sweeper became accepted. Originally, without a bag vacuum cleaners had a noticeable real advantage over with a bag vacuum cleaners. The HEPA filter that all without a bag vacuum cleaners have stops just about all the dirt and odors from leaking out the vacuum sweeper exhaust. The good news was that the HEPA filters stopped dirt from spewing out. The bad news is that the clogged up rapidly. They clogged faster if the air had high humidity or if you were picking up pet hair. The pet dander sticks to the filter and restricts air flow. The slowing air flow is also what cooled the motor. The motors in without a bag vacuums tend not to last as long as with a bag vacuum cleaners because of this restricted airflow to the motor in without a bag vacuum cleaners.
My wife and I own a retail store offering vacuum cleaners and filters in Wooster Ohio. The two primary reasons consumers ask us about without a bag vacuum cleaners is: 1) They want to save money on bags, or 2) They want less dirt. Bagless vacuums need a HEPA filter to stop the dirt. These filters are very effective. They also really need to be changed no less than once a year (more often if you have small children or pets) and, they aren't cheap, $29 - $59 each. It is not possible to spend as much for paper liners. High filtration paper liners may cost you a dollar or two apiece. You will throw away less money on the bags than for the without a bag filters, even if you change the bags frequently.
Less dirt? Do you own waste cans at home? Do you use garbage can bags? Why? Because it's far more clean when you throw out the bag instead of dumping the can with all of the dirt being thrown into the air. Mainly high end vacuum cleaners now utilize micron filtration liners along with a HEPA filter at the exhaust of the vacuum sweeper. The micron filtration liners offer exceptional filtration, and they don't clog up and restrict airflow like the HEPA filters in without a bag vacuum cleaners. The HEPA filter at the exhaust takes much longer to get filthy because the dirt and pet hair is trapped in the high filtration paper bag.
Less pricey vacuum cleaners are almost all without a bag. The profit is in the filters, not the disposable vacuum sweepers. The higher end vacuum cleaners almost all use high filtration inner bags.
If you have pets, the pet dander is what sticks to the without a bag HEPA filters. We also urge to pet owners that they use a vacuum sweeper with a charcoal filter to trap and neutralize the pet odors. Also, natural fiber brushes on your vacuum sweeper's roller brush will not trap the pet hair in the carpet tool.