Time Machine in Mac OS X Lion initiates local backups called snapshots, OS X Lion keeping additional backup locally on the Macs primary hard drive but this can be a real pain if you are trying to conserve disk space. Time Machine local backups are only stored if you have Time Machine enabled in general.
Below is the instructions to turn off local backups:
1. Launch Terminal from /Applications/Utilities
2. Enter the following command:
sudo tmutil disablelocal
3. Enter admin password when requested to disable local backups
To re-Enable Local Time Machine Backups, perform same steps as above except with following command entered into Terminal instead:
sudo tmutil enablelocal
After perform above steps, you will not have local backups anymore. It’s important to have regular backups of data and so if you’re going to disable this be sure to still use Time Machine, perhaps even initiating manual backup before disconnect the drive in order to preserve recent copy of data.
You can refer below link for more detail information about Time Machine.
Mac 101: Time Machine – Get to know the ins and outs of Time Machine.
Time Machine: Troubleshooting backup issues – If you are having issues with Time Machine backups, learn how to troubleshoot them.
Software Update – Get the latest updates for Time Machine.