Being on the road (or just away from your Time Capsule) for longer periods of time may cause a surprising dent on your free disk space counter. As time marches on, those who have Time Machine enabled will soon realize that something is eating away precious disk space. On Macs with relatively big hard drive space this should not be an issue, but those of us using Airs are always keeping a sharp eye on the available drive space.
Spending some time away from my TimeCapsule caused the MobileBackups local storage function to kick into high gear on OS X El Capitan: soon enough, it was eating away ~12 GB of space. But what exactly is it?
MobileBackups local backup storage
If you are not connected to your TimeCapsule for a longer period of time, Time Machine starts to use up percent of your available free space and builds up a makeshift local Time Capsule backup of sorts. This serves as a last-minute resort to recover something from deletion, but only if it has been changed from (or added to your system since) the last time you were connected to your Time Capsule. It is a pretty nifty idea to keep you protected from accidental file or directory removal at the price of eating up free space. Mind you, if your overall free space drops to a certain percent, OS X will start purging the oldest elements in this local Time Capsule to give back some free space.
Can this be disabled?
Absolutely. If you don’t want Time Machine to decide how to use your free space and neither do you want the local backups, just open the Terminal and issue the following command:
sudo tmutil disablelocal
after which you should reboot and voilá! MobileBackups are no more.