Let’s say you have a codebase X, and a codebase Y. X produces some results or does some logic that are needed by codebase Y. What should we do to get the results (for this exercise, let’s say it’s a JSON file) from X to Y?

• Shared file store (box, onedrive, s3).
• Live service (e.g., an API).
• Monorepo: Y can run X’s code from the same repo to get the JSON.
• Distribution packaging (pypi, internal artifactory, cran, npm): Y can import X, run it.
• Many repos on a single computer: Y and X are next to each other, run X separately and get the files or import it locally. I've seen this done without the use of git submodules, but this is the use case for submodules.

Where I work, we use all of these strategies when the situation calls for it. Each situation is different, so let’s outline some of the considerations that may come up:

• Security and permissions: can the user of Y have the inputs to X? The code for X?
• Is there a team to support an API?
• Does the organization and the users have the structure necessary to handle a monorepo?
• How many people using Y need the output from X? Is it just some code functionality they need?
• Are you in a place to plan and maintain a strategy?

In lieu of telling you how to chose, I'll just leave the options and those questions to help you decide!