Out of the box artefacts that read this property. Append the path to your instance URL to open the record and see how the value is used.
ACL script: kb_category
When the setting is exactly true, a failed write check for the current parent is followed by a check for the parent record; otherwise, the first result stands. This code shows no different behavior for users and admins, and it supplies no default value.
/sys_security_acl.do?sys_id=b1815a10d702210013ab49547e61031a
ACL script: kb_category
When the setting is exactly true, a failed create check is retried against the parent record; otherwise, creation remains denied. This applies to users and admins alike, and no default is specified.
/sys_security_acl.do?sys_id=c24be1e0d702210013ab49547e6103ac
ACL script: kb_category.parent_id
When set to true, the check requires the user to have create access for the selected parent; otherwise, it allows creation without that check. No default is supplied, so a missing property also allows creation without the check.
/sys_security_acl.do?sys_id=5d924bf99f882210ecf142a4ba0a1c83
ACL script: kb_category.parent_table
/sys_security_acl.do?sys_id=cdc24ff99f882210ecf142a4ba0a1ca1