I run 12 flow on my wands, but just last month I bought a 1.5 inch wand with 6 flow on it just for the rentals and small trailers and such. I get so tired of fighting 2 inch hose in tight places and in empty properties where the drying times don't matter as much.
My rental turnover season hasn't hit yet, and I won't know for sure until I have cleaned with it for awhile, but I was surprised at how little difference 6 flow had when compared to 12.
I haven't cleaned a really trashed out place with it yet, and I suspect I will quickly drag out the larger wand when I do, but the moderately soiled places have been just as easy to clean with the smaller wand. Makes me wonder if the high flow might not be more bulletin board hype?