Even if your Furniture doesn’t look dirty, it probably is.
If you want to find out how much soil is actually on your furniture that you think “does not look dirty”, simply take a white terry cloth towel and put it over the end of your vacuum hose. Turn the vacuum on (don’t let the vacuum suck up the towel). Gently massage the fabric with the cloth. If you have a round dark spot on your towel, that is embedded soil in the fabric.