This is a common myth that the commercial pet food industry would like you to believe. Our grandparents and great grandparents fed their companion animals with raw scraps from their own meals because, at the time, there was no such thing as bagged kibble and canned pet food. However, pets should NEVER be given cooked bones from leftover meals from their human companions. While raw bones are easily digested and utilized for important calcium and minerals, cooked bones are dangerous and can cause blockage and/or bowel perforation.
Dogs and cats are carnivores and have the jaw structure to rip tear and swallow prey animals. They do not have flat molars like humans meant for chewing grains and whole vegetables. Their digestive tracts are short and manufacture very harsh gastric juices meant to digest whole raw meat and bone and move it through their system very quickly. So, in reality, feeding your pet our raw food is feeding them human food but it is formulated into a carnivorous, species appropriate diet, close to what they would get when eating a prey animal.