Primarily, you will use Active Directory Sites and Services to manage domain controller replication. You can force replication between domain controllers.
In a home domain, you would most likely use a single domain controller, so it would not be very important for you.
Sites are also used to give the client a priority when looking for a domain controller. The client computer will use a domain control in the same site as the client machine first, then if no domain controller is available it will look for a domain controller in another site.