Yes, the pre-difined layout line was the one reason I could think of for using an off-centered reference. A center line has always been related to my use of a Japanese carpenters square. Line up the square on the ink line, trace along the opposite edge, flip it over and mark the other side. It has always been good and consistent for me. Another reason, more idiosyncratic, is that a center line is, well, centered. No consideration of left or right, east or west, north or south, up or down, the movement of the sun or rotation of the earth and other pit falls. Maybe I exaggerate... but like I said it suits the broader peculiarities of how I work.

Any other advantages of using an off-center reference line?

Greetings,
Don Wagstaff