It's your choice, and you can also allow other people to connect to it. The standard settings gives an experience that is close to the real game (as of WotLK), but you can tweak these settings to level faster or whatever you want. Depending on the implementation you go with, there are different ways to add new content - one of them (Azerothcore) is for instance very addon based and you can add bots or difficulty scaling to make things soloable for instance.