What is "incomplete-pieces" folder for? All my torrents are completed. But if I delete this folder, tixati commences to download something unknown.
This folder takes much space on disk, I wish I could know of its intention (designation).

I have wondered that too.  http://support.tixati.com/settings%20-%20transfers%20-%20local%20files  gives an answer:

Incomplete Piece Storage

   This is where the software will store small fragments of downloaded pieces before they are complete. The data is stored separately because only complete pieces can be hash-checked for integrity, therefore it would be dangerous to save this data into the main downloaded file. This location should have at least 40-50 MB of free space available otherwise data may be lost between sessions.

I am having trouble though with understanding it takes up too much disk space. I have been using Tixati for several years and yet my folder for incompletes is under 8 MB total, hardly enough to be concerned about.

> du -hs .incomplete-pieces/
365M    .incomplete-pieces/

That's mine and it's only that big because I stopped a bunch of torrents that I have had running before.

Actually for me this is issue also. I have much space on my HDD BTW 960MB allocated by this folder. This is not good. All torrents had been finished but as soon as cleaned folder some torrents became incompleted and they started to download again.

There are also "dnd_file_crust" files stored in this folder. These are "boundary" pieces of files selected to download. Tixati has to download whole pieces, when you select some files in a torrent, Tixati saves the rest of boundary pieces in incomplete-pieces folder. The folder may be big, it depends on number of selectively downloaded files, piece size, file sequence in a torrent and so on.

Go to locations change incomplete pieces storage location to default