Nothing gets built exactly like the drawings. In the case of my addition, the spiral stair did not fit, and there was no place to get hot air from the first floor to the second. This required some big box structures in the pool room. I am aware that all this is on computers these days. The ideas remain the same.
Computers make it easier to keep a paper trail of changes.
A control system like CVS is much like this. Except in the software case there can temporarily be many different Empire State Buildings. In the hardware case there is only one. The hardware case is a little differentin in that at any time you can go out to the real Empire State Building and see what is actually there. Lots of things get covered up.