I just finished watching Why Google Stores Billions of Lines of Code in a Single Repository and honestly, while it looks intriguing, it also looks horrible.
Have you run into issues? Did you love it? How was it/
I think it mostly has to do with how coupled your code modules are. If you have a lot of tightly coupled modules/libraries/apps/etc, then it makes sense to put them in the same repo so that changes that ultimately have a large blast radius can be handled within a single repo instead of spanning many repos.
And that’s just a judgement call based on code organization and team organization.