When should I create a new Primary DNS Zone?

In an Active Directory domain with a single primary DNS zone and integrated DHCP, every DHCP client will register themselves with the server holding the primary DNS zone when their lease is renewed.

If there are a lot of clients, or if the WAN links are very slow, couldn't this cause problems? Would it ever be a good idea to create a new primary DNS zone in a different location? Alternately, what would be the reasons against creating a new DNS zone?

VERY few reasons to have more than one primary zone. Seriously. This is - in the context of AD - more a leftover. Well, not really...

• Multiple domains in one forest MAY have multipe top level domains, though it is technically not necessary.

But at the end, it is so because DNS supports it.