For convenience. So you can view your video without having to retrieve the original copy from the SD card on the drone. Might come in handy for recovery too, if you were unlucky enough to lose your drone during a flight.
It can also records audio from the device your using (iPad, Android, iPhone)....I guess if you wanted to narrate the footage or provide details of your location.
Thanks for the answer! Forgot to mention another main detail.
Does it draws battery life from the ipad or whatever connected to remote at time of flying and recording? Thanks in advance!