Listen, for PvP there's no secret. It's a very mediocre spec with little pay off for its worth. Unless, of course, you enjoy tab dotting and bolstering your ego across the scoreboards over useless damage numbers - go for it. As far as killing and control power goes, there are other specs that outclass it in every way imaginable.
I personally look at the buffs and my character lighting up for the proc.
It has a steep learning curve, but as I said before - barely worth it. It's a lot different vs a Watchman sent, who, by all means: pays off quite well for its ramp up.
You couldn't be more wrong, tab dotting as madness sin won't give you any high numbers whatsoever. It's a lot stronger dps spec than deception but requires a lot more skill.