Here’s one that just came to our attention the hard way: we were recording a drummer playing a Roland TD-20 kit. Along with capturing the MIDI output so we could apply various drum libraries during the mixdown process, we also recorded the stereo audio out from the TD-20 brain, intending to use it as a reference track. As it turned out, the Roland sounds worked perfectly — and now we wish we had recorded the separate audio outs from each TD-20 instrument so we could have put each drum on its own track for further processing and editing.

Moral of the story: always record everything, and if possible, record individual outs so that you can access individual sounds later.