One arrow is great shooting practice. I also just started shooting one of those basketball-sized Rinehart targets that you just throw out somewhere. Knowing that a miss means I'm probably going to have to search in (and under) the grass, I tend to focus better.
The best shooting I've done in a long time was last week, at Compton. I have only shot one other time on an outdoor 3D course; usually I practice with 4 arrows, in my back yard. I was much less sloppy, more focused, and more consistent at Compton, where I got one arrow for each target.