Some commercial steam cleaners have an agitation feature to dislodge more particles. This combination of high pressure and a high temperature effectively dislodges particles that have been cleaning to carpet fibers. The professional will use a truck-mounted steam cleaner in most cases to propel heated water and steam into the carpet.
Steam cleaning carpets is preferred by many people because it only uses heat and pressurized water or steam to remove ground-in dirt and other particles.