Share 'Double twist in tsukis'

I have always been curious about the double twist of the hips when punching advocated by several styles of karate. I have heard couple of reasons for it, but none which really convinces me as to the merit of the double twist. One was, in case the punching hand was grabbed you wouldn't lose your balance. Can anyone provide some insights? How is it applied in kumite, in particular full contact styl…