We teach our children the rules of being indoors and being in public. We teach them to use inside voices. We teach them not to "rough-house" inside and if they get to carried away, it could result in them braking something or more importantly injuring themselves. We teach them to be polite and respectful in public; that the same rules apply in public as they do indoors. They are taught being outside in the yard or on a playground is the time and place to be kids and run wild. But of course rules and safety still applies.
When teaching our dogs it is the same way for them. You teach them that they are not allowed to get rough inside because they can hurt someone or themselves. You teach them to not jump on the furniture. You teach them that outside is where they are allowed to play and run around. It is important for dogs to understand the rules and to obey them. It keeps everyone safe and happy. It is a constant reminder you are their leader.