IGNORE is generally used in very specific situations:
* Some records are managed by some other system and DNSControl is only used to manage some records and/or keep them updated. For example a DNS record that is managed by Kubernetes External DNS, but DNSControl is used to manage the rest of the zone. In this case we don't want dnscontrol to try to delete the externally managed record.
* To work-around a pseudo record type that is not supported by DNSControl. For example some providers have a fake DNS record type called "URL" which creates a redirect. DNSControl normally deletes these records because it doesn't understand them. IGNORE will leave those records alone.
In this example, dnscontrol will insert/update the "baz.example.com" record but will leave unchanged the "foo.example.com" and "bar.example.com" ones.