Room or Room ID is the required field for the Partner role and optional for the Owner and User roles. Basically is the Publisher ID that you can see in the VT Publisher and VT Receiver.
Owners and Users may not have Room ID, which leads to the following:
Control Panel will ask you to enter the Room ID. If you do that you will be able to see and manage the streams from the Publisher with entered Room ID. Note that the Room ID you want to enter must be known in your Main Account User License List.
You can do the similar as the above with the VT Receiver and Publisher. Just change the ID in the apps and you will be able to publish the streams to the receivers with entered ID or receive streams published with the same ID.
If the Owner or User has the Room ID they can't change the Publisher ID in VT Publisher. Can change Publisher ID in the VT Receiver, but only to the Access ID of the particular stream, which leads that Receiver with that license will work in one-channel mode.
Partners must always have the Room ID. It will be applied in the Publisher, but in the Receiver they can only use the Access ID of the particular stream.