Large bore / Small bore - What diameter size differentiates?

You asked for an answer based on my experience. First I need to clarify what my experience is relative to this specific question.
I do not remember ever working on a project where we did not route all sizes of pipe. By routing the pipes I mean that we made Piping Plan drawings (one exception*) which showed all lines and drew Isometrics. My experience as an "on the board" designer and supervisor was before computers, it was all manually drawn. It was our company culture. It was done on projects that were EPC (Engineer, Purchase, Construct) by the company. It was done on jobs where the Field Construction was all Sub-Contracted by others. It was also done on Modular projects. It was based on total material control, cost control and "Quality Assurance".

The exception noted above was a very small job where we only made a physical (plastic, wood and wire) model and Isometrics. Even here we had isometrics for all line sizes.

Why do people not draw isometrics? Well today you do not need to create isometrics if (BIG IF): If your Client agrees to it. If you have created the design in 3D and shown ALL lines. If all Field construction and installation will be done by a different contractor than your company. If your Client has paid for installing a workstation (with a trained operator) so the sub-contractor can look at the model to field route the small lines or download their own isometrics. If the sub-contractor agrees to it. If the jobsite is located where there is ready access for additional materials. The "IF" list can go on and on.

My opinion: I think "Not" routing all lines and producing isometrics and not doing full and proper material take-off and procurement is false economics. If I were the Client I would demand that ALL lines were routed and the material provided. That one small line may prove to be the key to the successful operation of my plant.