The Double Sinawali is the skill where you learn how to wield two weapons simultaneously without getting your arms tangled up. This skill can also be applied to single weapon and empty hand as well.
Recently it seems to me that deceptive hand skills has been very popular to learn in knife combat, like a new fad. In these styles there are techniques taught that are specifically designed to be deceptive. What many people may not realize is that when you learn various forms of Double Sinawali and put them together so that you can free flow, your arm movements naturally become deceptive. Since your free flowing you are unpredictable and smooth which gives you speed. The reason I never emphasized that Double Sinawali will make you deceptive, is because it is not the main purpose, that is just a by product.
The main purpose of the Double Sinawali is two fold. In Training it is a generator that allows you to include various techniques and put everything together in one smooth concoction. In combat it is used for multi-purpose, much like a Swiss Army Knife it is handy and can do many things. Defensively it is a parry on steroids. Right now criminal knife styles seem very popular today in the martial arts community. These styles are very aggressive and all about assaulting someone. The Double Sinawali techniques can be executed very aggressively too, it's just that it is not taught this way because I think most martial arts focus on self-defense or knife fighting. Knife fighting often times has been ridiculed. But I think it is underrated. I believe that a true martial arts warrior is someone who expects to face someone who is better than themselves. In other words a trained and worthy opponent. If not, your basically a bully and far from a warrior. So when facing a worthy adversary you cannot be so aggressive, you have to time that and be much more careful and strategic.
Criminal knife styles I believe do not want to give their target this much respect, so they will not give the target even a chance to fight back. If there is a potential, they will probably choose another time to attack, because they do not want to fight, they want to assault and victimize.
So in my opinion learning how to trick and destroy a weak person is much easier than learning how to defeat a worthy adversary head on. By learning the Double Sinawali you can use it for both purposes.