I started using them again and it seems fine. You're ok as long as you use it for things like external library projects and not splitting your project repo into smaller bites just for the sake of doing it.
That's exactly what lots of people want to do.
Would be nice if it worked like the development mode of Python's packages: I can install a local development copy of the dependency somewhere, the main program will see the changes I make and therefore it's possible to develop both at the same time.
https://github.com/git/git/commit/95c16418f0375e2fc325f32c3d...