We use our furniture multiple times a day, hundreds of times a year. All that use and traffic, both from you and your family (including pets), add in a little bit of dirt, grime and whatever else that may have been brought in. A simple wipe or vacuuming of furniture is unfortunately not enough to fully clean it.
That method may remove the surface stains or crumbs, but upholstery is like a sponge and absorbs all the bacteria and grime. Unless it is periodically deep cleaned by a professional, you’ll be sitting in all that stuff that can negatively affect your health and allergies.