This is a question I even asked myself prior to getting our trusted sub contractor in to do ours. I hoover every day without fail, we have a shark, we don't wear shoes, they can't be that dirty right?! Wrong!!  
I've had people in to clean my carpets before but the results were nothing compared to this time around! They literally look brand new. Previously I stood and looked at the carpets afterwards and they looked fab, stains appeared to have gone however the next day once the carpet had dried there they were! These were not stains like blood or red wine just general foot flow dirt. I had a conversation with another company we work closely with and he said to give him a try, more expensive but the equipment used justified this price. A truck mounted beast with high temp extraction, industrial drying fans and all the knowledge of carpets to go with it! I can definitely say my carpets were not clean, I saw the water! But they are now! Also don't be fooled into thinking you can hire a rug doctor and do it yourself, it could make things worse and cost you more in the long run! Go for it, treat your feet and your carpets, you won't be disappointed!