Reference to Wikipedia-Win8
What is this device encryption feature? What am I missing by choosing Pro or RT?
Device encryption refers to the ability to protect local device data from offline hardware attacks by employing encryption. This is achieved by employing a file-based encryption filter. The master key for the encryption is protected with the user’s device lock PIN.
When device encryption is enabled, during bootup the user is prompted to enter the PIN. Until the PIN is entered, bootup is suspended.
In windows RT you get the device encryption which is definately a plus if you have some private data.