The first time I ever heard of "the rod" was a shop fitter who said they'd be given full size drawings on a roll to lay out flat on site, in situ infact, and work everything from them - no scrabbling around with tapes, pencil marks etc.
Then I learned about them on a C&G course - probably the single most important thing: full size sectional drawing on a bit of board, drop your components on it and take marks off, for everything; lengths, mortices, haunches, hinge pockets, every detail. No measuring involved, no error (if the drawing was right to start with), easily repeated (in a stack if possible) and so on.