There are a lot of carpet cleaning methods out there. Some are pseudo dry, or low moisture, and some are true dry methods of carpet cleaning. This video shows a pseudo dry carpet cleaning method. Although, they are using a dry compound for the cleaning they still used a pre-spray to emulsify the soils that allowed the cleaning compound to pick it up.
The biggest issue that I have dry compound compound cleaners is that there is no way to extract the the cleaning compound effectively. Here is a picture of my cleaning equipment after cleaning a home in Tampa FL. The carpet cleaning service my customer had previously used cleaned with dry compound carpet cleaner. The carpet was soiled but looked fine until a started to clean it. All of the cleaning compound that was still in the carpet started to come up.
A ton of the dry carpet cleaning compound was still in their carpet slowly collecting soil and attracting dirt. At Chem-Dry of Tampa FL we use a low moisture steam cleaning system to remove soil while minimizing moisture. Our cleaning system is not a dry carpet cleaner that uses a compound to remove soils. Our cleaner is an extremely effective hot carbonated extraction process that removes soil and drying within a few hours.
I'm not saying the dry carpet cleaning is not effective but I know that I don't want a dry cleaning compound lurking deep in my carpet holding on to soil and bacteria.