What does the BitTorrent setting clean?

Anyone know?

[bitTorrent]
ID=2173
LangSecRef=3022
Detect=HKCU\Software\BitTorrent
DetectFile=%ProgramFiles%\BitTorrent\BitTorrent.exe
Default=true
FileKey1=%appdata%\BitTorrent|*.old

this show the bitTorrent section cleans the .old files from the bittorrent section. However as I don't use BT I don't know what those files are

*.old files are typically a configuration backup that's made each time the program runs, well at least they are in uTorrent.

Thanks for the answers guys.