Assuming I understand what this is doing correctly, it does the reverse of a submodule.

git submodules let you tack a second git repo onto an existing one. For example repoA tracks `repoB@version1234` at path `/foo/bar/baz`.

This on the other hand lets you take monorepo and checkout `/go/mysubservice` as a "repo" and treat it as its own repo. Then when you do git pushes etc, it translates the changes into the larger monorepo.