Anytime I had multiple dogs its because I was doing rescue. But I think a good reason to get another dog is because YOU want another dog to work with. Generally with the bully breeds people own multipules because of the love of the breed, or are active with the breed (Showing, Raising, Agility etc). But its never a good idea as a general rule of thumb to get another dog based on companionship for your current. It just must be something YOU want to invest your time into.