Starting with Lion I noticed that Time Machine is running even when my Time Capsule is not available. I also noticed that Finder shows a different amount of used disk space than
df. My MacBook Pro’s SSD also got somewhat slow. Turned out it’s Time Machines MobileBackup function.
If you want to disable MobileBackup and free up the abused disk space, simply run the following command and reboot.
sudo tmutil disablelocal