It’s a lot of work, as starting over is often easier than reviews and edits. Usually the diagrams are slightly out of date, but good enough to satisfy whoever is looking at it.
I wish I had a better solution. Now I’m wondering I could write something that walks the code for me.
For a presentation or project documentation artifacts, I can then go thru my sketches and pull bigger pictures together easily. I applied Fowler's "sketch" principle in my own tool ormle.com
That way, the diagram source and
Do use diagrams to explain an abstraction, and attach a word to it. Don't use diagrams to represent the exact state of a system.