WE, as a crew, snap lines every five courses. I might not pop all my lines on sections with an easy frame of reference, but mostly I do.
Fix the C & P!
And yes we snap lines. Every 6 courses. Not only better than eyeballing, but much easier too.
I said my piece back then. We still strike lines, but I don't do much roofing any more. The guys that don'[t strike lines do it way too cheap. IMO