It is separated from the main game files so users can save bandwidth and disk space if they don't want the music files.
If you only want to play the game and don't care about having the music files in a separate folder (like MP3 or FLAC), you can skip downloading this file entirely. fg-optional-bonus-ost.bin
The file is an optional component found in FitGirl Repacks , a popular site for compressed video game installers. What it does It is separated from the main game files
If you include this file in the same folder as the installer ( setup.exe ), the installer will give you the option to install the soundtrack along with the game. Helpful Tips fg-optional-bonus-ost.bin