Lots of homeowners mistakenly think their carpet and furniture are clean simply because they appear so. But with time, even the cleanest-looking carpets and upholstery can slowly lose their original shine. They collect dust and dirt beneath the surface, a place where regular vacuum cleaning might not get to.. Therefore, to increase the useful life of your carpets, most carpet manufacturers recommend you have carpets cleaned every 12-18 months before you may recognize they are dirty. This routine ensures cleanliness, even if you don't notice the dirt.