Plantuml plugin within Confluence is pretty nice for documentation, and arguably a super-power because it makes it easier to make good docs ("a picture is worth a thousand words").
The source shows up in edit mode (no external app needed; and it's always correct) and it handles the rendering for you, thus reducing friction.
In other places I've seen people attach a PNG. If you're lucky, they've also attached the corresponding (and up-to-date) source in visio/draw/ppt/whatever random app format, in which case making a small edit might only takes ten of minutes. In the worst case, it's missing source, the source file is not the same as the PNG, or they used some program you don't have, and you have to totally redo it. For most people if the friction is too high, it just doesn't get updated.