Is it worthy to turn on File Vault?

Solution 1:

Do you run the risk of loosing your computer? Is the information stored on your computer of high value to other persons?

If your answer is no to these questions you should not consider using FileVault 2 as it has some drawbacks:

• The encryption happens on the fly. As your C2D processor does not support hardware accelerated encryption, your CPU load will increase. Newer CPU's like the Sandy-Bridge processors support that Apple ships support AES-NI instructions for hardware accelerated encryption.
• Your I/O tasks will become slower for the same reason. Even witth AES-NI support the performance slightly decreases. But in your case the effect should be a lot bigger.
• Auto-login is not possible with Filevault 2 enabled.

Time Machine

Time Machine does not encrypt backups per default. Even with FileVault 2 enabled. You will need to enable encryption with Time Machine. In Lion, FileVault 2 did not support encrypted wireless backups but work-arounds were possible. Mountain Lion supports wireless encrypted backups to Time Capsule.

Solution 2:

It's worthy, especially for a portable device. In case of theft you don't have to worry about someone getting access to your files. Even if you don't carry around the machine there's still the possibility of theft from your home.

There're basically no performance penalties noticeable. This would only matter if you do something like live video editing of 4K video or something. But in normal operation it's not noticeable. And the process of first encryption has become really user friendly by making it on the fly, meaning you can continue work on your machine while it encrypts everything in the background.

As for Time Machine, you should additionally encrypt your Time Machine backups to be fully safe in the home theft case. You do that from the TimeMachine options for your backup drive where you'll find a checkbox labeled "Encrypt Time Machine Backup".