Time Machine in Mac OS X Lion initiates a sometimes useful, sometimes not feature: local backups. Called snapshots, this seems to be kicked off when your primary Mac is a laptop and the Time Machine backup is an external drive, so OS X Lion compensates for the potentially unavailable external disk by keeping an additional backup locally on the Macs primary hard drive. This has its obvious advantag
![Disable Time Machine Local Backups in Mac OS X Lion](https://cdn-ak-scissors.b.st-hatena.com/image/square/26f13d4547d72dcee303bf34743b5e5975491c7d/height=288;version=1;width=512/https%3A%2F%2Fcdn.osxdaily.com%2Fwp-content%2Fuploads%2F2011%2F09%2Ftime-machine-local-backups.jpg)