They allows Nexus owners to restore their devices back to stock
Google released Android 4.2.2 Jelly Bean update for Nexus devices earlier this month and now the search giant has published factory images for these devices.Nexus 4, Nexus 7 Wi-Fi, Nexus 7 3G, Nexus 10, GSM Galaxy Nexus yakju and GSM Galaxy Nexus takju have just received their Android 4.2.2 Jelly Bean factory images.
According to Google, “these files are provided for use in restoring your Nexus device's original factory firmware.”
Keep in mind that in order to take advantage of these factory images, users will need to have the fastboot tool in their PATH. In addition, the Nexus device needs to be in fastboot mode, with the bootloader unlocked.
For more details on how to download and use these Android 4.2.2 Jelly Bean factory images head over to Google Developer site.