Such a dummy interface has no identity (ip/dns/port) but is sufficient for host creation.
New items might be automatically assigned to an existing dummy interface if the host lacks of a proper regular interface. Items assigned to a dummy interface may be treated like disabled as requested in ZBXNEXT-1924.
On creation of first regular host interface Items currently assigned to a dummy interface might be re-assigned properly.
Removing a regular interface that is still used by items might lead to re-assigning them to a dummy interface if such exists.