What is the significance of .TUF file in Log shipping?
One of the user has been confused to see lot of .TUF file within their server where the log shipping is enabled. Basically this .tuf file is the Transaction Undo File, which is created when performing log shipping to a server in Standby mode.
So if you ask why standby mode, database recovery is done when the log is restored and this mode also creates a file with the extension .TUF (which is the transaction Undo file on the destination server). In this mode we will be able to access the databases. and also refer to this KBA http://support.microsoft.com/kb/308774 about further information.