In the process of documenting this engine, I mapped out what the difference was between the 2D program I had been using with my new 3D parametric design program (Solidworks).
Sometimes you have to put things on paper to be better able to understand the process.
The drawings I made for this engine in 2D CAD are not related to each other dynamically, and so if a change is made to one part in 2D, one must be very careful to update every view of that same part, and also one must update any part that mates with the part you changed.
With 3D modeling, if I change a part, all of the views of the part in the 2D drawings automatically update to reflect that change, and by viewing the assembly, I can tell how the changes affect mating parts.
Everything in 3D modeling emenates from the 3D models of the individual parts, including the Bill of Material, the Exploded View, the 2D drawings, the motion study, etc. Any change in any model is automatically and dynamically changed in every other entity, most importantly in the 2D drawings.
3D modeling is a quantum leap in design power, and I have likened it as ranking in importance in the design world to things like the creation of the wheel, or the creations of computers themself.