Identify Discovery Methods in SCCM 2012

When you plan to use discovery in Configuration Manager, you must consider where to run each discovery method.

After Configuration Manager adds discovery data to a database, it is quickly shared between all sites in the hierarchy. Because there is no benefit to discovering the same information at multiple sites in your hierarchy, consider configuring a single instance of each discovery method that you use to run at a single site instead of running multiple instances of a single method at different sites. 

The following table identifies at which sites you can configure the different discovery methods:

Discovery method	Supported locations
Active Directory Forest Discovery	Central administration site Primary Site
Active Directory Group Discovery	Primary site
Active Directory System Discovery	Primary site
Active Directory User Discovery	Primary site
Heartbeat Discovery	Primary site
Network Discovery	Primary site Secondary site

Secondary sites cannot configure Heartbeat Discovery but can receive the Heartbeat DDR from a client.

When secondary sites run Network Discovery, or receive Heartbeat Discovery DDRs, they transfer the DDR by file-based replication to their parent primary site. This is because only primary sites and central administration sites can process discovery data records (DDRs)

Ref.: http://technet.microsoft.com/en-us/library/gg712308.aspx