I think grandparent is talking about something else. Large C++ codebases often have a guide that says which parts of the language to use and not to use. That can be useful if you have a team with people with different levels of expertise in the language, or expertise in different parts of the language. C++ has grown to be a language with a lot of different parts to choose from.

And it looks like Python is heading in the same direction. It's not difficult to imagine a future where some Python projects are going to want such guides too.