Your carpet and furniture act as filters to collect harmful dirt, dust, dust mites and their bi-products and all types of bacteria. If you don't clean these filters periodically they will start to contribute to an indoor pollution problem.
E.P.A. Recommendation
The Recommendation from the Environmental Protection Agency is that you vacuum everyday and have your carpets and upholstery professionally cleaned by a hot water deep-extraction system once a year. Also studies have shown having the cleaning professionally done is 15 times more effective in removing the containments.