I don't find it a source of confusion, because my boxes and lines diagrams are explicitly meant to be sketches, and are presented as such. UML, as others have

I don't find it a source of confusion, because my boxes and lines diagrams are explicitly meant to be sketches, and are presented as such. UML, as others have said, is both too precise about things that are still vague at sketch time and took vague about things I want to be precise about to be useful. And once I have a real system, the real complexity in the system always makes for either an insanely huge diagram with lines everywhere, or an imprecise one full of lies and omission. Trying to program with UML is basically like trying to write a system of 10k lines by first writing them all down, and only then beginning to try to compile it. It's not going to produce good results, not just because of the endless little errors, but especially the big ones that your could have discovered much sooner if you were using something more real than UML. UML is superficially easier to work with than direct code, but in depth, I think inferior to it. Some of the notation is sometimes useful, but to use it as intended is crazy.