Explanation on SCCM Discovery Methods - What exactly they discover?

1. Heartbeat discovery
It pings all the machines existing in the network, i.e domain and workstation group machines are discovered automatically and shown under "All Systems" collection. If we enable Heartbeat Discovery, the discovery data is refreshed on a schedule that you determine. If we disable Heartbeat Discovery, the discovery data is refreshed only when another discovery method is invoked or run on a schedule.

2. Windows User Account Discovery and
It discovers all user accounts in same domain.

3. Windows User Group Discovery
Windows User Group Discovery is useful for creating group-based collections for software distribution

4. Network Discovery
Network Discovery discovers the client operating system only if the computer is configured to share resources. It discovers the following-
Topology
Topology and client
Topology, client, and client operating system

5. Active Directory User Discovery
It discovers the following:
User name
Unique user name (includes domain name)
Active Directory domain
Active Directory container name
User groups (except empty groups)

Note: We should run Active Directory User Discovery only on primary sites.

6. Active Directory System Discovery
It discovers the following:
Computer name
Active Directory container name
IP address
Assigned Active Directory site

Note: Polling performed by Active Directory System Discovery can generate significant network traffic (approximately 5 KB per client computer).

7. Active Directory Security Group Discovery
It discovers the following:
Domain Local Security groups
Domain Global Security groups
Universal Security groups

Note: We can run Active Directory Security Group Discovery only on primary sites. It polls Active Directory for all system resources in its database, including those discovered at child sites, and including secondary sites. Because Active Directory Security Group Discovery does not contact the computers directly, the computers do not have to be turned on to be discovered.

8. Active Directory System Group Discovery
It discovers the following:
Organizational units
Global groups
Universal groups
Nested groups
Non-security groups

Note: We can run Active Directory System Group Discovery only on primary sites. It polls Active Directory for all system resources in its database, including those discovered at child sites, and including secondary sites. Because Active Directory System Group Discovery does not contact the computers directly, the computers do not have to be turned on to be discovered.