CN=Users Container:
GPOs: Group Policy Objects (GPOs) cannot be linked to this container because it is not an Organizational Unit (OU). GPOs can only be applied to OUs.
Default Location: New users are created in the CN=Users container by default when using standard Active Directory tools unless specified otherwise.
Other Options:
Users outside this container can log in.
The container can contain both user objects and user groups.
Users created here do not need to be moved to log in.
Reference:
Active Directory Containers and OUs