You only need to worry about the scale when you are doing floorplan diagrams, and the like. For other diagrams, I go with no scale, since it doesn't matter that makes the most sense.
The scale is a conceptual aspect of the page, and is only used when you are drawing something where exact size matters. For most network diagrams, this is irrelevant because it either doesn't matter (logical diagram) or because the rack diagrams (physical) go off RU size, and are contained within a cabinet or rack. It doesn't affect the printing size.
