I was taught to pre-vac, pre-spray, agitate, dwell and extract - yes it's long winded - yes you have to take several pieces of equipment into the premises, but as far as I am concerned I am doing it the right way, by the book.
Having said that, when I was recently on an NCCA course there were cleaners there who put powerburst straight into their machines and then scrubbed away with the wand - they assured me that they get good results and all their customers are delighted.
To my mind this goes against everything I was taught, not to mention what the cleaning solutions are doing to their pumps and the lack of a rinse afterwards - but hey, whatever works for you.
Not the way I would do it, but they are not my customers, so not my problem.
Steve