1. PDF is to become a standard CAD interchange format.
2. Using PDF where 0.03% matters is insane.
3. If CAD requires 0.03% tolerance, then using PDF as a standard CAD interchange format is insane.
I would imagine you generally want arbitrary precision for CAD.
I cannot imagine a CAD system that can't symbolically represent what is actually desired. The model and its spec should be one and the same.
Approximations also open the door to different precision versions. Not helpful when different parts from different sources need to be consistent.
Models that approximate/vary from the ideal spec, created intentionally to match manufacturing limitations, are ok.
For laser cutting, I prefer to use SVG, as it's easier to generate. I had not really thought about precision, but SVG can represent circles directly.