What are sites? Are they important?
Sites assign a computer joined to a domain to a default Domain Controller.
If you have multiple subnets in your environment with DC's on each subnet, the Unix server is not assigned a domain controller. This may result in sending network traffic across a costly WAN link which may be cross-country or out of state. Sites are determined by IP address. In Active Directory, an administrator would make a subnet mask, and assign that to a site.
Then computers in that site would be able to obtain a list of DC's for that site from DNS. These site servers are assigned as default.
When using sites, your servers in California talk to your Domain Controllers in California, not the Domain Controllers in New York.