Ability to delete existing managed hosts prior discovery
When there is an existing managed host, discovery process either fail or pass depending on if the existing host has the same MAC provisioning address or just hostname. Hostnames must be unique (due to DNS) however MAC addresses do not. There was a setting to change the behavior to error out explicitly or just ignore and allow discovery of hosts with different hostname but conflicting MAC address.
There is a third solution and that is often asked "delete existing managed host when it exists". This is dangerous because it allows to delete hosts via discovery API, so this feature comes only with explicit setting.