Each admin node will have one instance of shove, and each admin node can be managing multiple projects. For example, the generic and engagement clusters both host many sites but each only have one[1] admin node that handles all the projects in the cluster. Thus, that instance of shove is running commands for many projects and needs to be told which one it is running commands for.

`[1]` I'm pretty sure it's one. It might be two. But it's definitely not one node per project.