Balance of Trade contains radical changes to the trade routes mechanics. Trade Routes no longer provide scaling yield that can easy get into the high teens. Trade Routes provide a much more consistent and smaller yield that is more proportional to their production cost and similarly costed buildings. Internal trade routes also provide bonuses to new cities that help it get started but go away once the city builds a trade depot and can stand on its own.
More information can be found at the discussion thread.
More information can be found at the discussion thread.