Hi.
Basically what this does it that you can use one set of jumper cables more than once. You know there is a 30min or 60min CD on the cables? Well, if you die in an instance and you luckily have two players with high enough engineering skill to use it, have player 1 try to ress another player from the group. If he fails, give the jumper cables to your engineer friend and have him try it. As it is not BoP or BoE you'll be able to trade it ;-)
Have a nice day.