The thing that hits me again and again about lots of drills is that what we are learning (or simply ingraining, creating a habit without any awareness) is rarely what we think we are learning. That's huge for instructors, too-- You may not be teaching what you think you are. There's a video out of some instructors 'woofing,' screaming horrible, rude things in student's (largely women) faces. The instructors are certain they are conditioning women to the emotional context of an attack. But the women are practicing, rep after rep, letting a threatening individual invade their space, take a position of physical and psychological dominance, and the women practice doing nothing.
Sparring, at any level, is a special case. Humans mistake intensity for truth. Things that trigger bigger reactions- fear or anger or exultation- simply feel more real than than the drudgery of day to day. In almost any given martial art, sparring is the most intense training methodology and feels 'more real' than any other exercise. Humans rarely question such a natural feeling. Most have never had their roulette table moment.
That means that any bad habits learned by sparring are learned deeply. And there must be bad habits. The essence of martial arts is the manufacture of cripples and corpses. If you have never crippled or killed anyone in training either what you do doesn't work or, more likely, you have also learned flaws with every drill. Those flaws are critical in any live training. Never forget that you are practicing at least as many reps of not hurting people as you are of hurting people.
Sparring is not a fight simulation. Maybe most types of sparring are intended that way and certainly people believe that they are, but the math doesn't work. At some point two oiled-up guys in speedos of the same weight getting together face to face without weapons at an appointed place (without obstacles) and time to work under an agreed set of restrictions somehow became 'reality fighting.' It's not, and if you feel a need to defend it as "as real as it gets" take a deep breath and think for a second.
So lets start there. MMA contact sparring/competition. It covers a lot of skills and it is pretty damn effective at what it does-- which is prepare you for MMA competition. I don't think that's it's real purpose, though. The real purpose is deeper than that. There has been a long evolution of coming up with the best venue for testing ourselves. Boxing and wrestling always tested the essence of manhood-- strength and speed and endurance and toughness and smarts. By making it broader, MMA added an incredibly valuable level of mental flexibility. MMA deepened how far you can go with strategy. At higher levels all contact sports are strategy sports. MMA took that to a new level. If you want to find out who you really are, MMA is the way.
There is lots in there that applies to self-defense. Same with any of the contact martial sports. People who get hit regularly have a huge advantage over people that don't (until the concussions start to add up.) People who actually hit moving targets are way ahead of people who hit air. The fact that it hurts... damn, people, fighting hurts. It shouldn't be a revelation to anyone. And pain is a great motivator to train harder.
It's good training, but it predicates on bad strategy-- equal people, weapons, techniques, location, no surprise. All that jazz. If this is your gig, be sure to spend some time working solutions when you give the opponent 50 pounds of weight advantage and your back. It can be done, it has been done. But if (again) you have this urge to come up with excuses about why it is impossible, you've confused the game (MMA) with the solution.
Similar stuff goes for all the heavy contact stuff. Boxers are formidable fighters because they are used to taking and giving hits. There is something fundamentally fucked up in martial arts if being 'used to taking and giving hits' is special. That's the natural environment of a fight, people. That said, there is also something fundamentally screwed up about a fighting style that has its own fracture. When boxers do use their skills in real life far too often their hands are shattered. Outside of the safety equipment (tape and gloves) the essential weapon of boxing is more likely to hospitalize or cripple the guy using it than the guy it is used on. That's a whoops. What does boxing develop? Courage, and that is huge.
Moving and controlling a body is one of the core skills of fighting. You will learn this in a grappling art (especially one with throws) better than anywhere else. It is huge and important. It makes everything else easier ("Position before submission!") Good grapplers/throwers will also teach you much of what you need to know to handle bigger and stronger people, especially if they are old-school enough to practice without weight classes. Definitely spend some time here... but it is not fighting. In a fight, moving and controlling a body is intended for another purpose, like escape or disabling. In order to get really good at grappling, people often forget the context-- bad guys and weapons and obstacles and "Why am I here?"
As a general rule, if your grappling changes a lot when the other guy has a knife, you were probably a little too caught up in the game side. Or, to phrase it another way: If you grapple differently when the threat has a knife you were probably doing it wrong when he didn't.
And then straight non- or controlled-contact kumite. This was the big epiphany in Minnesota, at least as regards sparring. Marc has a drill he calls the 3-2-1. I will probably misrepresent it here. For the pure version, work with him. But my understanding (or misunderstanding) is damn useful, so here it is:
There are ranges and positions where someone can stand and hit you without any telegraph. The threat has to be in range (drop-step exception) and have their limbs in certain positions. This is a code red thing, or what Marc calls "1". The bad guy can hit you in one motion.
For the most part that's not true. Even in range, most positions require you to shift your center of gravity (CoG) before delivering power (again, there is an exception for the drop step. I love the drop step). Marc calls this a "two". It will take two motions, a precursor and the attack itself, to do you any harm.
"Three" means the threat has to change his foot position (and the drop step, in certain positions turns all three to a one... very cool) as well as shift CoG.
I spent a lot of time in close proximity to very bad people. More than a few commented on how relaxed I was. It's powerful. Relaxation can be disconcerting, it makes the criminal think that you know something he doesn't. This was why I could do that. Not only could I tell if the bad guy could reach me, I knew, in advance, exactly what he would have to do or where he would have to shift his center in order to attack. I knew when I was safe and I knew exactly what to watch for should the threat try to move.
These are critical skills in point sparring. Minor, maybe, and nothing like what I though I was learning (timing and strategy and ...) But killer skills in the real world.