Someone I know recently was told by their veterinarian to give it to the dog after the dog had gotten into chocolate candies (ate, wrappers and all). It did cause the dog to vomit the candy, and saved probably hundreds of dollars in a trip to the vet ER.
We spent the night at a cabin which had rat poison out in little cardboard trays. We forgot about it when we brought our dog in for the night. We woke up to the sound of her scooting the tray around. She had eaten it all.
We called the number on the poison box and the lady told us to make her swallow hydrogen peroxide. Amazingly there was a bottle in the cabin. She took two swallows and vomited everything up. We took her to the vet the next day and they put her through a course of Vitamin K. She suffered no ill effects from the experience.