Dogs are a great way to get more exercise. They require several walks a day, which gets the owner up and about in the neighborhood and meeting the neighbors.
Studies have shown that the biggest deterrent to crime is just knowing your neighbors. We certainly wouldn't know as many neighbors as we do if it wasn't for Amber. Just by walking around the area a few times a day we get to see and chat with the people living nearby. So we know who lives around us, and who doesn't.
Also, seeing people walking around the area is a deterrent itself to crime. People generally don't break into cars when someone is walking on the same street. Same with houses.
And, of course, houses are less likely to be broken into when a dog is in the house. Although there has been a disturbing trend in DC where dogs are being cholorformed by burgulars. But still, it is a good general rule.
Dogs are the first animal to be domesticated by man. They have evolved alongside us for thousands of years. It is a natural relationship that benefits both parties.