The game plays its music because thats part of the game itself.
On some occasions it won't be in a special compressed all-in-one resource file but raw wav or mp3 files which you can just snag/copy to wherever you usually put other music albums. Buying the additional soundtrack does require you to own the base game(sometimes) but if you get all the files from the game itself it might not be worth the extra purchase. However its nice to have all the music only sound files where you can get to them, say if you put them on a shared server in the back corner of your room and not have to install steam on every machine just to play those files.

Nope, buying a soundtrack doesn’t affect the in game music or sounds. The game already comes with its own audio. Soundtracks on Steam are just extra downloadable files (usually MP3 or FLAC) you can listen to outside the game, like in your music player. You don’t need to buy it for the in-game music to work.

wow it means it is useless XD
Thank you guys , Have Fun <3

引用自 xxxFuryX：

wow it means it is useless XD
Thank you guys , Have Fun <3

Well if the games music isn't loose music files you're going to have to find a tool to extract it which might be impossible. The soundtrack purchase would be for that particular situation.

引用自 xxxFuryX：

wow it means it is useless XD
Thank you guys , Have Fun <3

Yeah, who buys music anyway, right? I mean, being useless and everything.

Взаимный +rep