In residential, I'd assume you'd want full coverage so heads in the attic and conditioned space. To save money, you'd stick with a dry system. You could run the plumbing inside the conditioned space and keep it wet but you'll see the plumbing, etc.
I've seen conditioned spaces in commercial freeze due to equipment mailfunctions, etc. Saving grace was shutting the system off before it blew. It would be one more thing to worry about at home when on vacation, etc. Remember the stretch of negative weather we had this past winter... I was checking 1st floor/main level ceiling temps daily because no building is that air tight.