I found the explanation over the page on how the VCU works more help.
With little differences in speed the jelly stays liquid and the VCU doesn't do anything. When the front and rear shafts spinning speeds are a lot different it heats up and locks solid. So if you could get the jelly out it would never lock. Think that was Datatek's idea.
Of course, as Wammers pointed out, if you hit some mud and you're going to have fun!
Personally I still like the idea of a proper difflock.
See post #19.