When you play in this way, its simply about deciding which Setting you what to play in. The campaign settings are all defined on this site and you build a list following the restrictions placed there. Typically the lists are richer in character and there will have been an attempt to balance the list itself, and among its peers. The object is to give exciting games with balanced opponents.
Settings are all community contribution, so if you have feedback or want to do a new campaign setting please lets hear from you.