This metric counts the number of principals who are members of the sysadmin fixed server role. SQL Server relies on role-based security to manage permissions. If multiple IT system administrators have permissions to set up new SQL Server logins, they might be inclined to do so as part of the sysadmin role. Adding a normal user to the sysadmin role could pose a security risk and is not recommended unless the principal is highly trusted. See Server and Database Roles in SQL Server (MSDN).
The associated alert will be raised if the number of expected principals goes higher than the threshold specified. This is useful if your organizations doesn’t have the ability to use Audit Specifications or write triggers for new user creation.
If you want to set a different threshold for each SQL Server you’re monitoring, install the metric and follow the instructions on Customizing settings in Configuring alerts (SQL Monitor documentation).Principals with sysadmin login,