Git can host multiple DAGs in the same repo with git checkout --orphan command. A frequently cited use case this feature of git is to keep separate a branch for docs or the GitHub gh-pages orphaned branch for creating a static website.
Are there other reasons to use orphaned branches in git?
Another possible use of this is for combining multiple repositories into one. A few examples:
In these cases you will have two separate DAGs in the same repository before they are merged into a single unified tree. Thus this is not as much a long-term use, but an action that will temporarily pass through the state of having separate DAGs in the same repository.
Another use case by the git online documentation:
This can be useful when you want to publish the tree from a commit without exposing its full history. You might want to do this to publish an open source branch of a project whose current tree is "clean", but whose full history contains proprietary or otherwise encumbered bits of code.
