Default DNS entries at domain creation

[rolo@]

I currently use the DNS server at the same box where Plesk is installed, so I let Plesk manage the zones.

Having said that, I have two domain names that act as nameservers, so that every time I register a domain name that I will manage in the Plesk box, I set the name servers to these domains.

Having said that, whenever you create a domain, Plesk adds two DNS entries like this:

ns.example.com. A 1.2.3.4
example.com. NS ns.example.com.

(1.2.3.4 would be the domains's IP)

Do I need these entries? What are they for?

Regars,
Rolo.