Like a writer's rough draft, a song goes through countless edits and re-edits as demos before the finished product finds itself on an album. Sometimes big changes are made once a band is settled into the recording studio and begin to play. The Rolling Stones originally wanted "Start Me Up" to have a more reggae feel to it, until four years in the recording studio turned it into the song we know and love today. In most cases though, it's just a tweak or two that comes by way of the producer or sound engineer meant to "clean up" a song and give it a crisp finish. These demo tracks, or first cuts as they are sometimes called, often get tossed out and forgotten once the band discovers the perfect sound, records it and calls it a day.
In some cases, bands save their demos and first cuts to be released as promotional material for a forthcoming album. The songs are let free into the realms of the internet and find their way onto various music blogs, tabloids and websites taken as evidence for what to expect next from the band. We sit and listen to these first cuts as the band heads back to the studio to work the final nooks and crannies for another, better release.
[Personally I enjoy the Tennis demo versions better than the actual album tracks]
TENNIS
demo/first Cut released on CAPE DORY [2011]