Wrong I'm sorry Ian.
Who's the experienced valeter? :

Not by just rinsing with pure it won't do too much harm.
But by rubbing pure water in with your wfp brush you
will take the polish off, and hence take the protection and gloss from the car.
If it's takes grease and grime off a filthy window it's not going to have any trouble with a layer of polish!
I've tested it out myself, and there's
definately less shine after wfp.
Also I can see tiny little scratches all over my van from where I've been lazy and wfp'd it.
But I always try to polish it once a week at least to counter this.
If you look at any company car (like a BMW 3-series) you see little scratches and swirls from where it's been through car washes, using brushes.