Walking tall and having the fitness to run away are the only self defense skills anyone will learn from a group MA BASED FITNESS class. They are important skills...especially moving with confidence. That can stop a would-be attacker in his tracks if you look like more trouble than you are worth.
If you want self defense, you train in self defense. If you want tournament skills, you train for tournaments. Martial arts are great stuff, but sparring and the real deal are completely different. The adrenaline you get from being in the ring is NOT like the body and mind jolting adrenaline that occurs when the real deal happens. I've only experienced that sort of adrenaline a couple of times, and it takes a TON of effort not to freak out/wet your pants/panic. I worked in a correctional facility, so the encounters I've had have never been one on one and in a completely uncontrolled environment like the streets...and yet the adrenaline surge is still completely unforgettable. It's nothing like the constant low level buzz of adrenaline you get from sparring. It's harsh, it's immediate and it's nearly overwhelming.
I know I constantly have to remind people in my kickboxing classes that it's not self defense. I may use imagery to add to the aggressive essence of the class and to sharpen their focus, but punching a bag isn't like punching a real person and it doesn't prepare anyone for any sort of self defense. If I wanted to do that, I'd have to buy a redman suit and attack my participants. Which would actually be fun, come to think of it!