There is definitely a place for guardian dogs.  You can have a power failure. You system can be disarmed. Studies have proven that the average thief will not attempt to break in a home with a dog if if the dog has never been trained to protect,  defend, etc. Not necessarily because they are afraid of the dog. But because the predator thief doesn't want to be seen. Not only will they not enter your home they won't try the neighbors home. They will move on to an easier mark. 

I had a neighbor that stopped me one day to say something about my dogs.  I assumed that he was going to complain.  He thanked me for having the dogs. He said his home was being broken into about 3 times a week. The thief took out the entire window frame and would sit it back in making it appear that nothing was wrong. I had no idea this was going on. He showed me the window. Then he said no one has broken since I got the dogs. 

Although my dogs have a job and that's to protect my family and property it is not the dog that should be feared. The dogs will warn us. That's just one line of defense.