Schematic design has been part of the CAD world since its very beginning. Both schematic and layout for the IC and PCB realms were two major directions used in the CAD world.
For a decade or so the schematic design for electrical wiring creation in terms of the harness engineering became part or CAD and the new eCAD – electrical CAD – quickly and easily became its own realm.
The design of electrical schematics and harness designs is a big challenge for many companies, while taking into account one thing:
A piece that big and that complex is definitely the most expensive component of the machinery.
Wiring schematic design in Excel (or on paper) simply cannot keep up with the current complexity. Also, the harness design needs to generate accurate reports and BOM lists, which cannot be rendered in simple sketching tools. Well, one may try, however the quality of the entire design process may not be guaranteed.
A small anecdote
There was a big aeronautical company that designed aircraft without using proper tools for the eCAD realm. Nevertheless, the harness was manufactured and was ready to be fitted into the airplane; unfortunately, the harness was too short !!!
Or maybe the airplane was too long ??!