I shampoo my carpets about every 2 months. I have kids and dogs and they need it. I can't imagine leaving all that dirt in there and never getting it out, yuck! And just saying you have dogs, doesn't mean they are pottying on the carpet, it just means they are tracking in dirt.

With the snow melting and the mud that gets tracked in this time of year I need to do mine again. I've had a shampooer for 10 years and I've never had a problem with mold.