When you download a torrent (Ubuntu ISOs for example...), you usually want to contribute some upload back into the torrent (I think a 1:1 ratio is preferred, and 1:0.5 [DL:UL] some kind of street avg. minimum?)
So, I just happened to try to seed a torrent from my Trash folder. If you're like me, you like to download stuff to your Desktop to later process it as you see fit. Once I've moved my stuff around, I trash what's on my desktop. But now, I still want Transmission (my fav torrent client) to seed that.
Complete your download and copy your files around. Leave your downloaded copy on your Desktop.
Click the little gear icon on your torrent, then click Move data file to...
On OS X, go to your home folder, then press Command+Shift+G to bring up the "Go to the folder" dialog, then type ".Trash". Do the same kind of thing on Linux or Windoze.
That's it. If you just remove your torrent from Transmission, your files are already in the Trash and ready to be wiped out.