The original stain removers

Every 6 months or sooner.

No ! Would you wear your pants for a year straight and never change them ? No you would not ! Your carpet gets traffic from several different pairs of shoes that hold the flu and cold virus on the soles. and the impacted dirt wears your carpet out faster. 

It could yes ! the problem with those cheap machines, is that they do not have enough power to extract the water it puts into your carpet, therefore your padding turns into a sponge causing mold and bacteria.