In FTK, when you view the Total File Items container (rather than the Actual Files...

Total File Items includes files that are in archive files, while Actual Files does not.

Total File Items includes all unfiltered files while Actual Files includes only checked files.

Total File Items includes all KFF Ignorables while Actual Files includes only the KFF

Alerts.

Total File Items includes files that are in the Graphics and E-Mail tabs, while Actual Files

only includes files in the Graphics tab while excluding attachments in the E-mail tab.