Just that really. We have a gsd, a great big fluff ball and muck spreader. She does bark occasionally and can look very menacing if you are a leaf or a cat (cat must be a minimum of 3 feet away).
Someone coming up to the door or even walking straight into the house can do so safe in the knowledge of either being ignored or greeted with licks & tail wags.
Luckily we didn't get her for security, good job as she'd be crap. Unless we got burgled by a tree or the local moggy 
Anyone have an equally useless canine companion?