Pre vacuuming, pre spraying with a micro splitter, agitating & rinsing is in most cases for me far the best method for cleaning carpets.This technique ensures all the carpet fibres and therefore soil is in contact with your cleaning solution and doesnt require over wetting, so drying times are kept to a minimum. Another Plus with this approach is the clean water rinse, thus leaving the carpet free from residue which is a good sales point to make with customers when performing surveys.
Paul