"Starting here [main.cpp :: Start()], how do I end up here [Frobnificator.cpp :: FrobnifyQuux()]?" - should give me a sequence diagram like this one: https://s.plantuml.com/imgw/img-f05ecfe23bf545656a3a1f66b2a9.... And then I should be able to narrow it down, skip selected functions or classes.
I once spent over a day drawing such a diagram (much larger) for the core system of a large codebase I started working on. I did it by manually stepping through a codebase and making notes as I went, in PlantUML format. It ended up being tremendously helpful, as parsing a diagram like this is much faster than parsing textual representation. And a year later, when I had to revisit that part of the code again, despite being not entirely accurate, the diagram was still very helpful.
Same for other types of diagrams - class, state, component, activity, timing diagrams. The tools we have all have enough information (e.g. Clang definitely understands C++ codebases well enough that it should be able to spit out the aforementioned sequence diagram between two given points), but I'm not seeing them used this way.