Soapy
An extractor is only part of the carpet cleaning process:
a. 85% of the soil in carpets is dry and you remove it with a very thorough vacuuming before putting any moisture into carpet fibers
b. 15% is oily soil on the fibers.
c. After vacuuming you remove stains & spots using appropriate stain remover chemicals: protein, tar & grease; rust; red dyes; coffee/tea and pet stains and a steamer preferably.
d. They pre-spray with a foaming carpet shampoo and let dwell to emulsify the oily soil on carpet fibers.
e. Then friction scrub with hand brush or rotary shampooer
g. Now you extract to remove the residual stain remover chemical, oily soil and shampoo residue. You can either use plain hot water or add an extractor chemical which is high dilution, like 64 to 1 to rinse clean.
There is two camps on this, plain water or extractor shampoo, it seems to be a matter of preference.
However, do not think you can clean carpets with only an extractor you have to follow this procedure which is the process advocated by the Carpet Cleaning Institute of America.
Regards