Back in the stone age, not that many years ago, computers either didn't exist or the ones that did shouldn't be and weren't anywhere near audio. Studios had a recording medium (multi-track tape), a mixing setup (mixer and outboard gear) and a mixdown deck (a 2-track tape deck.)
When CD's became prominent and digital masters were needed DATs were sometimes used as a mixdown deck. It took a while for that to catch on because you skip the step of the mastering tape and you are bypassing the opportunity to digitize with a mastering engineer's superior convertors. Still, it became more popular with a burgeoning new class of studios- the project and home studios because it saved money. Burnable CD's didn't exist, yet.
Time wore on, however, and today the home/project studio tends to digitize the tracks right after the preamp and its much easier to mix on the computer, bounce the mix to a stereo wave file and burn it to CD as either a data backup or an audio CD. That's a very different process than multi-track deck->mixer->mixdown deck.
Standalone CD recorders are still *very* useful in any outboard rig with live shows being the most obvious. I did a live show at an audio school here and was given a DVD and audio CD within 15 minutes of ending the performance! Only possible with a realtime external burner. At least I don't know of any software that can do that with a computer's CD drive. Also useful as a mixdown deck for those studios that aren't computer based or would rather not run their mixs back into the computer and fuss with them *again* in order to deliver a CD.
-C