I have noticed it is possible to publish some services without any layers (i.e. no LayerIDs are discoverable). I am trying to publish a parent map service without any layers, because the child service will be created by enabling a server extension.
Example here
If the parent map service is configured to have no meaningful data (i.e. it serves as a 'dummy' service), this can seek to point users towards the child service. This is particularly useful if both services carry the same or similar names.