Greetings,
Lets say I have a group of devices, that I could name Company1. That group would always hold all the devices and I could then just simply give a user permission to be able to view that specific group. Then I could also add individual devices for that user to see.
It would not be requirement for a device to be in a group, but instead I would be able to sort routers into specific groups.
This would give me much better user control and overview what devices specific user is able to view.