A device can be marked as ignored. If it is marked as ignored, it will not be imported into the SARAH system. For SARAH, it is nowhere visible on the services, gateways in the Web UI and the apps.
Difference to a deleted physical device: a deleted device will be imported again from a gateway, when the endpoint is synced again.
Why? This feature has been introduced in SARAH 2.2 to keep devices outside of SARAH, that are not relevant for the SARAH system. For example, gateway-specific devices that should be ignored, or non-used spare physical device ids can so be specified and never touched by SARAH again.