I never use my (Karcher) pressure washer for this, because of the possible problems already mentioned and because I'd worry about a) dislodging trim and b) forcing dirt up under trim and into other hard to access areas.
I do understand the rationale behind the idea and I'm sure not saying it won't work, just that it's not the approach I take.
When my vehicles are really dirty (and believe me, the minivan gets truly *awful* some times!) I use the foamgun with a BHB. I just *barely* touch the panels with the BHB, blasting foam through the bristles all the while. I don't press hard enough to bend the bristles over and I don't "swipe" the BHB across the panel, I sorta "jiggle it" so that if there *is* any marring, it's only gonna be maybe 1/4" long. I suggest repeating the mantra "dislodge and flush" to keep in the proper mindset

(no, no, J/K)
And I still rinse the BHB out and dunk it in the shampoo bucket even when using the foamgun. I might go over a panel many times this way, gradually and *VERY GENTLY* dislodging the dirt. Then I wash again with mitts. And if there's any chance my mitt isn't rinsing clean I get out a fresh one. Any tenacious dirt that won't come off gets clayed with
Sonus green and I wash the panel again after that. I carefully inspect each panel after the final rinse before moving on to the next one.
It's not easy, and it's sure not quick, but I can usually get through (a tough Ohio) winter without significant marring.
BTW, using a slick LSP helps immensely.