Digital SLRs are basically made to only do one thing very well, and that's taking photos. Beyond that, though, it's pretty much useless for editing those photos or sharing them until you get to a computer.
The modded battery grip still clips onto the bottom of Hunt's Canon 5D Mark II, despite all the extra parts. The on-board computer doesn't do anything to improve his images, but it does let him wirelessly tether his camera to a PC via a Wi-Fi dongle.
While the camera is connected to a Wi-Fi dongle, Hunt can remotely control his camera using a networked PC or a smartphone, and he can even wake it using the remote trigger. The Camera Pi also allows the camera to directly back up its images to a USB flash drive, as well as set up a custom intervalometer with programmable camera settings.
Hunt wants to further modify his battery grip by adding a small screen and an internal power supply for his Raspberry Pi board. Seeing as he's already accomplished so much, these additions probably will be no problem for him.