I recently purchased a backup drive and began using Time Machine. My initial backup was quite lengthy as expected. However, now each time I back up, if I have used my virtual machine through parallels my backup is around 75GB which is way too big for subsequent backups. I am running Parallels 6. I set the back up configuration to "optimize for time machine" and took a snapshot of the machine and tried to back up again and once again the back-up was around 75GB. When do the snapshots reduce the size of the backup? Is it on the initial back-up (once i change the settings to "optimized for time machine") or is it on subsequent back - ups? Should I back up once more at 75GB then expect quicker - smaller - backups?