At its core - its using the right amount of pressure for the job.
No more. No less.
Many do it yourself'ers or inexperienced pressure wash companies will simply rent a washer - and start spraying.
That's a sure fire way to damage your screens, roof shingles, or siding.
With soft washing - there is no need to blow out your screens or pop off your siding with less effective & more damaging high pressure.