So I am new to Time Machine - and I fully understand its use, etc Question though... Say I have a 640 gig HD backed up via time machine. Say I have 500 gigs of that HD used Say 20 gigs is a edited video file. Now say I re-edit the video and use the same name. When time machine does it's thing I assume it just copies the changes.. so would that mean that my 500 gig backup is now 520 gigs as it will save the new version/retain an earlier one? If so - If I change a lot of video files - the odds in me filling up the external quickly are high, right? I know ultimately Time Machine will remove older versions (older backups). But it this correct as I've laid it out?