Microsoft introduce a new feature in Outlook 2013, that allow you to limit the mailbox history that can be saved in the offline cache.
From what I know, the new feature could also be controlled by using Office 2013 GPO (Group Policy Object).
The new feature provide the following advantages:
a. Reducing the disk space that require to save the offline cache.
b. In case that the computer was stolen from its owner, the mailbox data that may be expose to unapproved persons is limited to X months.
c. In some cases, the Outlook performance may improve, due less I/O to the computer hard disk.