Eyes Only is a security feature for ServiceNow records, so only those associated with the record can view. This is helpful when your organization has sensitive information that does not need to be seen by others outside a select few.
The guide is to help ServiceNow admins setup Eyes Only to limit who can see designated records. The goal for Eyes Only is to work in conjunction with the default out-of-the-box (OOTB) ServiceNow role base security model to insure future upgradeability across ServiceNow releases.