In the knife combat community it has become popular to study the knife "fighting" methods of the bad guy. It makes sense to me that you should know the tactics of your possible opponent. The famous legendary swordsman Miyamoto Musashi wrote in his book that you should know the tactics of your opponent, and I totally agree.
Like many modern combat styles, this kind of no-nonsense combat styles are very popular. People feel that these kinds of styles are superior to what is traditionally taught. When they say no-nonsense, let's examine what they mean.
Usually they are referring to exercises and drills. If it doesn't work in real life, then your wasting your time. Many traditional martial arts are meant for long term training, and they have many developmental exercises. These exercises are parts to a whole, and when examined individual they may have no combat application, but when combined with the other parts they become practical and effective. So if you remove such exercises from your training, then you become very limited in how much you can grow.
If you ignore all the other things found in traditional martial arts and focus only on no-nonsense combat, then your not getting the whole picture. There are some people who can function well without the whole picture, however they can only go so far with limited knowledge. Also if they encounter problems they may not have the tools to figure it out.
Bad guy fighting techniques are designed to bully and cheap shot their prey. It is designed to assault a person weaker than themselves. Compare that to traditional knife fighting. Traditional knife fighting is designed for you to face another trained knife fighter. The self-defense techniques are generally designed to defend against a knife while you are empty handed, which is a tremendously disadvantageous position for you. To me martial arts has always been about being able to defend against someone that is superior to me, if not I am a bully, and I do not think that bullies are good fighters or worthy warriors. Can a bully still be effective? Without a doubt, and that is what makes the world a dangerous place, a noble warrior can lose to a bully. There is no guarantee who will win.