http://support.tixati.com/Settings_-_Transfers_-_Metadata

Under Settings/Transfers/Metadata there is an option to set a folder for "Delete after Loading"

What functionality does that provide and how can it be used purposely?

If the torrent metadata file is deleted on loading, is then a copy incorporated into the active tixati database, which on removal then leaves no copy of the .torrent file at all?

After the .torrent file is loaded into Tixati it is no longer needed by the program unless you 'remove' it from the list and your computer and want to re-download whatever the torrent was. This auto-delete gets rid of the useless .torrent file from whatever folder you save them to when you download them off the internet. The entry remains in your Tixati list unless physically removed by you.
This saves space since the .torrent file is not needed and is just taking up space in your Downloads folder or wherever you save them to.