Well, I can't speak for the OP but the most common reason to need to do this is that, to burn a standard "Music CD" the spec says 16 bit, 44.1 kHz sampling, STEREO. If it's not stereo (or at least 2 track mono) it won't play in regular CD players (and many burners will refuse to burn it for you
But, yeah, no point in converting except for the final mix.