I mentioned earlier that that I only make rough sketches, not formal prints, for personal mechanical parts but I always document electrical projects of any size; here are some more thoughts on the subject. For simple parts like air gun nozzles, spacers, adapters, fixtures, etc., I probably won't need to make another one but, if necessary, I can easily get the dimensions from the original parts I made since they're still here. If I sold machined parts I'd certainly document them more formally, probably with AutoCad since that's what I'm familiar with. Electrical/electronic projects are a different story; once built, with the wires bundled & mostly the same color run to integrated circuits, enclosed relays & transistors, it's next to impossible to troubleshoot or modify them without a detailed schematic containing component pinouts after a few weeks, even if you're the builder &/or designer.