Because when another compressed format comes out, you don't need to re-rip everything again. You just convert the FLAC files (which are lossless) to the new format.

Or because you may want to consider using directly flac files on your empeg when you get a large enough hdd - so that you keep cd quality music in your car - and convert from those to mp3s for other players (except for karma ) which do not support flac (yet?). That's what I am planning to do when I upgrade my empeg drives, for example...