The Patient Attachments node in the sidebar displays all attachments associated to a patient. In Many mode this will display all attachments for all patients. In One mode this will display only attachments associated to the selected patient.
You may elect to have only a limited number of Patient Attachments load when in the Many mode. For example, you might choose to load only the last week's worth of Patient Attachments when in the Many mode. You may set this in Preferences > Attachments.
When in the One mode, all Patient Attachments for the patient selected will load.