In 0.14.0, If you do not add an ID then Multi-Scrobbler will automatically use the name of the Source/Client as the ID. The name is shown in the Dashboard.
If you decide to add an ID later, you must use the Source/Client name as the ID in order to keep Plays/Scobbles associated with the same config.
In 0.16.0+ you are required to have an ID or a configuration error is thrown.