The "Private Content" field in the Create Request form indicates that the nature of the requested work should not be made public.
It's already the case that the detailed problem description, ongoing comments, the record of changes, and a few other potentially sensitive things are private ('account number' and 'signing authority'). Marking an item as private adds the subject, summary and the cost estimate to the list of private fields.
When specifying this field in a customized sort or display, use the name "private".
Access to work information first requires authentication, typically to WatIAM. Once authenticated, one can always see all of the fields associated with items for which one is the requester, the owner, or responsible.
While the access controls are quite flexible, in practice there are only two additional possibilities that are used when one isn't directly associated with a work item:
While unusual, there are cases where privacy is justifiable. For example, a report of a security weakness, which if generally known would allow others to cause damage.
While it's usually not ideal, should there be a password in a work record, it's usually marked private as a hint to those with access to be careful.
And finally, should something not be visible to temporary staff, it should be marked as private.