What is is used for ?

Not officially announced but someone that works with DJI previously posted that the one by the tail can be connected to a computer and the onboard memory booted into a mode to allow downloading data. He also said the tool to allow that is not public.

The Micro USB port is primarily used to do Firmware up dates

Dan -

Not on the inspire. Currently its more of a diagnostic port or to transfer internal flight logs. All public release firmware will done by sdcard via camera.

the micro usb is used to do firmware updates on the controller with the sd card in the bird. and download flight data

Nope. The micro usb port for that is on the back of the camera ;) it mentions this in the manual.

Im sorry,  I thought thats what was mentioned,  My bad