The Involved Persons tab is for recording non-child parties to the case and other involved persons. The blue Add Involved Person from Contacts button pulls an existing contact from Address Book > My Contacts on the left side menu as a shortcut for persons you may add to multiple appointments, like case workers or therapists. This may provide a shortcut instead of creating each as a one-off contact on each appointment. The Add Involved Person button, on the other hand, creates a one-off, new individual for just this appointment, e.g. a family member. (You can also check a box to save an involved person to My Contacts.) Edit or delete existing Involved Persons via this Involved Persons table—but note, if you created the contact in My Contacts, you must edit it there.