I use mod.rs all over the place because it entirely encapsulates a module in a folder. But since the name of the file is fairly obtuse and doesn't say what it is, I usually only re-export other better named files that also exist in that folder.

I'm the case that I want a module with content, and then more further nested content that may use pub(super), I will use a module named file and a separate folder to hold it's children modules.