Older drives used to come with a audio jack and audio output pins on the rear along with play fwd/rew buttons on CDROM drives to play audio cds. Now the newer drives do not have a play button. Then whats the use of the audio output pins?
It is best if you use digital, as if you are doing something like ripping a CD to your hard drive, you may pick up noise from your system, plus you'll be removing digital error correction.