I think it depends on the Bully. I have litter mates a brother and a sister, and I brought them home together. They are company for each other, and they play together, sometimes only with each other. When we go to a park or leash free park with other dogs, , they will play and chase the other dogs temporarily, but then won't bother with them too much, they kind of stick to each other, they will chase each other, and play bite each others ears. Personally I think everyone should have more than one Bully, but it also depends on the personality of the dog, some dogs are friendly around dogs or cats , and kids, other dogs are not so friendly. I think you have to know the nature and personality of your dog, and what they like and tolerate. If you get your dogs together, and they grow up together , it's not usually a problem , or if your dog is well socialized you can introduce a new pet usually without any problems. But some dogs are best suited to be an only pet, as they don't tolerate other dogs, or cats, and may be more aggressive, this also might be true if you have an older dog and then introduce a new pet, they may not accept the new dog because they are kind of set in their ways or territorial , and used to being any only pet.