What DNS to specify when adding a domain to hosting and why?

Question

Domain Name System

There are several domains with different registrars. All domains have DNS servers of DNS hosting that we rent. Those. it turns out that all the necessary records for the DNS zone of the domain are made there. For example, we need to add a subdomain, we add the corresponding A record to the zone. But when adding a domain to the hosting, you again need to specify some DNS servers, usually the DNS of the hosting itself is already indicated there by default. But why do this when the DNS zone already has a record of type A from the IP server?

Answer 1

You need to specify the hosting DNS (not an A record, but so that the hoster has a DNS server for the domain), since only the hoster can know on which IP your sites are located.
Sites at the hoster can migrate from server to server and you will not follow this, but the hoster will follow and make changes on its DNS server to ensure the smooth operation of the site.