Today I learnt of this setting. I was seeing messages like the following on a couple of my servers and read the link:
1 remote calls to the SAM database have been denied in the past 900 seconds throttling window.
For more information please see http://go.microsoft.com/fwlink/?LinkId=787651.
This part gives you a gist of the matter:
The SAMRPC protocol makes it possible for a low privileged user to query a machine on a network for data. For example, a user can use SAMRPC to enumerate users, including privileged accounts such as local or domain administrators, or to enumerate groups and group memberships from the local SAM and Active Directory. This information can provide important context and serve as a starting point for an attacker to compromise a domain or networking environment.
To mitigate this risk, you can configure the Network access: Restrict clients allowed to make remote calls to SAM security policy setting to force the security accounts manager (SAM) to do an access check against remote calls. The access check allows or denies remote RPC connections to SAM and Active Directory for users and groups that you define.
By default, the Network access: Restrict clients allowed to make remote calls to SAM security policy setting is not defined. If you define it, you can edit the default Security Descriptor Definition Language (SDDL) string to explicitly allow or deny users and groups to make remote calls to the SAM. If the policy setting is left blank after the policy is defined, the policy is not enforced.
The default security descriptor on computers beginning with Windows 10 version 1607 and Windows Server 2016 allows only the local (built-in) Administrators group remote access to SAM on non-domain controllers, and allows Everyone access on domain controllers. You can edit the default security descriptor to allow or deny other users and groups, including the built-in Administrators.
So it looks like in my case some remote computer was trying to access this server’s SAM database (this is a server 2016 BTW) and it wasn’t in the local admin group of this server.