many uses for a dog like that. handler aggression doesn't equal unstable nerves or weak temperment. I personally don't like handler aggression and if stated right you probably shouldn't get any extreme cases like that. Some dogs come from places that couldn't handle a dog like that from the beginning and they've gotten out of control, only difference is when they're out of control they can do some real severe severe damage, it has nothing to do with weak or unstable nerves.
Extreme dogs are used for breeding, but must be paired with appropriate mates to get good offspring. Some dogs are used on tactical teams, once the handler aggression issues are dealt with. They aren't used as street dogs, some are estate dogs. Some dogs were simply the "big" dog so to speak and allowed to be that way for a long time and have only gotten stronger and more confident, no nerve problems, and those dogs can still make excellent patrol dogs. Its not a normal part of training, it isn't something that's routinely done.
That's why i kind of laugh to myself when I read about dogs not being pack animals, well when you haven't dealt with anything but a subordinate dog, you'd probably think that way. Dogs are pack animals and have pack hierarchy. They don't exhibit it much because they can read each others signals and fall into that rank and file. One steps out of line, they deal with it harshly. Same thing here, get a very dominant dog (extrememly rare) with no rules for a few years, then try do something that the leader would do, he'll put you right back into your place and it won't be pretty.