The "Start Over" selection on the MarketScanner File menu prepares a fresh view of the scanning file.
This is important to use if you want to try a different study on the data that was requested through the Preferences/Scan Settings screen and you have removed markets identified through previous studies.
For example, if you performed the Emerging Market Study explained in the Tutorial and removed all studies with low Z-Scores as directed, those deleted markets would be excluded form all subsequent studies unless you "Start Over" or rebuild the scan file through the Preferences screen.