This should be fun, prefrace for this: training is in quotations as i dislike calling it such. To "train" in martial arts by its literal definition all you need to do is any activity to aid your fighting skills. Right, now to start my rambling on the subject. So to begin with, i dont fully comprehend why it gets so much flak, somone generally does self study either alongside lessons or in lieu of them because they cant find anyone to teach them it. The obvious limitation is what material you are refering to when you self study. And if you can access any sparring partners and equipment. Pending what is taught, would also matter as some skills are obviously easier to pick up and retain, some others arent. Tieing back into the first statment, the only issues i see with it is: Quality and quality of material you are using. Both of which can vary in a school. This is a fairly short rambling as there really isnt much to write on the matter. Self study has its place and isnt a choice for some people. ie, like HEMA, the martial art could only exist in treatises therefor you need to disect the sources to learn it, and have to learn it from a book. If anyone else has any sort of rambelings on the subject, i forgot to cover diffrent sorts of media, but i dont think that has much of a place. As you should use it alongside doing it if you intend to learn any skills in this regard. That should fill in some blanks, and use (if possible) muiltiple diffrent kinds (of media). Addendum: I dont really know how to fit this in after writing but: Goals also matter to its usefulness, if your goal is just self defence, you dont have to fight proffesional boxers in a ring or combat athletes, just the average person. (now if the average person where you live is one of them, you probbly could learn from one of them ) In a similar way if you just want to loose weight and stay healthy you dont have to run a marathon, or get into bodybuilding, powerlifting etc.