Starting with Vista, Windows allows the recovering of previous versions of files without a dedicated backup. These previous versions are stored in "System Snapshots" as "Shadow Copies" whenever a Restore Point is made by the system or manually made by the user from the System Protection tab of the System App in the Control Panel.
Microsoft limited this feature in Vista to the Business Editions. Home Basic and Premium do not have it, hence the need for this program. It turns out in Windows 8...