Git submodules allow you to include one repository inside another, providing fine-grained control over dependencies and useful for situations where a dependency manager is not suitable. They are powerful tools that can be used to manage editable libraries that track upstream changes, or internal libraries developed within an organization. However, they come with some caveats, such as the need for manual updates and increased complexity in development workflows. Submodules are particularly useful when working with libraries not available through a dependency manager, or when editing the code of submodules is necessary. They can be used to automate tedious developer workflows by managing git Pull Requests (PRs) and continuous integration test (CI) runs, but require careful consideration of their use cases and potential drawbacks.