Selective downloading and Full allocation

[Nothingness]

I assume this has something to do with how bittorrent works? I only bring this up because I just today realized it wasn't possible with compact allocation, yet selective and full seems like an oxymoron. If I choose not to download something, the one and only reason is because I don't want that space being used. is this an impossibility on bittorrent? I'm guessing it has something to do with certain bits appearing at certain points in the stream?

[Nothingness]

ahhh nevermind, just learned what a sparse file was.