For those of us who do enjoy the advantage of dogs, here is an actual encounter:
Person at door: "Would you mind putting up your dog? He makes me nervous?"
Me: "The dog lives here. If he makes you nervous, you should probably leave."
Person at door: "Leaving."
In a more dramatic one, my dad's cousin had a salesman show up at her door, complete with panel van, saying he was a floral deliveryman but was having trouble finding an address in her neighborhood. This was in the late 80's, so before cell phones, and the guy wanted to use her phone to call the customer and get better directions, he said.
My dad's cousin didn't think twice about it, and let the guy in.
She hadn't even thought about her German Shepherd, "Pup," who was a sweetheart of a dog.
Pup took notice of this guy and started growling.
Salesman: "Does your dog bite?"
Cousin, finally getting a clue: "I don't think we want to find out."
When my dad's cousin called her husband to tell him what happened, he had her call the police.
She was surprised when several patrol cars pulled up. Turned out a serial rapist was targeting rural/suburban housewives by day, in the guise of a lost floral deliveryman.
Last dramatic example, my ex-wife had accosted a man who was choking his girlfriend in a parking lot near the bath house at Kailua beach, on Oahu. The girlfriend ran off, and the guy turned on my ex (we were married at the time; I was deployed to Bahrain). Luckily for my ex, who was all of 5'2", 100lbs, a crowd started to take notice, including some jarhead friends of ours, so the guy backed off.
A while later, my ex hops in the SUV she'd ridden in on, and she and our marine friends drive back to where she'd left her 4Runner. She drove back to our place, in a somewhat remote neighborhood in the Nuuanu rain forest - about a twenty minute drive, involving some unlikely turns. She went to the house, let out our Rott/Shepherd, and started to take her down to the back yard when the dog started growling, and moved in front of my ex.
That's when my ex saw the guy from the beach, and a buddy of his, approaching from the back yard.
Not sure what they intended, but doubt it was anything good.
They froze at sight of the snarling dog. The ex ran back into the house, and retrieved her previous year's birthday present from me, a Beretta 92 Brigadier 9mm.
The guys apparently left skid marks turning and running.
So, dogs, if you are a dog person, provide both warning and deterrent value. If BGs are not smart enough to leave, dogs also provide some damage capability.