There's a point of using it. People tend to think it will solve the ills of their under-capacity system but it doesn't. The best case is always the Alternator no doubt. I think that's why it gets a bad rap - using it for the wrong reason. Remember all Amplifiers employ capacitors in their system (digital ones are slightly different) but it's the same principal - stabilizing the voltage rail. Whether that translate to better sound is subject for debate. Employing one externally is no different. When properly designed and implemented, it does have merit.
As for dangers in a car, nothing is more dangerous than a tank full of gasoline underneath one...
