In my experience, the huge benefit of dogs is that they deter incidents. A criminal has no way of knowing how a dog will react, other than most of them react loudly. That, in it self, seems to discourage your average casual criminal, and they go looking for a quieter area for their shenanigans.
The other thing is that, in my experience at least, dogs are very sensitive to the owners' emotions. If the owners are friendly towards you, so are the dogs. If the owner is nervous or scared, then the dogs will be also. Two of our dogs will either lick a visitor to death or try to crawl in their lap from some ear scratching, including the 70+ pound boxer/pit mix. The German Shepherd mix is pretty relaxed most of the time (kinda too cool for school attitude), and is the only one we have inside when customers come over to pick up guns. There is no doubt he is the alpha male and right behind me and my wife in the "pack leadership." He usually finds a spot where he can observe from a short distance when strangers are in the house, so I have no doubt that the shepherd instinct would kick in if the "pack" were threatened.