I'm aware of the expressed negative potential of a power washer to "drive the salt into" crooks and nannies -- but I'm also aware that a garden sprinkler has never, ever, done a good job of getting rid of the salt for me. I've used both -- and the power washer will do more, get rid of more, help dissolve more salt. The salt is, remember, water-soluble, and water can get further into those little crevasses better when it's driven in by high pressure - better than when pushed at sprinkler speed. I've not used a sprinkler for more than six or eight hours, but when I've had it going that long (moving it, turning it, etc) -- there're are still very large deposits in far too many places under the truck.
But that part of the discussion aside -- whether I use the power washer to get rid of the salt or not, I still will be using it to get rid of the road grime and bugs (as mentioned) on the surface of the truck.