The jig mode is purely for downgrading from v3.50 to an earlier firmware e.g v3.41.
There is already a method of spoofing that will allow you to play a few games like assassin's creed.
GT5 is uncrackable so the only way to play is to update to v3.50 and buy the game. So when you what to use lets say homebrew then you can use the jig mode and go back to a firmware that supports jailbreaking.
As said before there is a possibly of jailbreaking v3.50 but it has not been proven.

Thanks again to MohammadAG

In regards to the bluray playback you should be able to restore that function by downloading these files and copying them to the required folders,
http://www.megaupload.com/?d=Y3AC4KME

in \drm put in the dvix folder
in vsh\bdplayer\ put in the two files
in \widget put in all the files