Here's what I've found from my reading. Engine calibrators calculate spark timing to avoid detonation at worst case scenario, which is low humidity. If humidity is higher than this, the spark can be advanced, which will result in more torque and better fuel economy.
I've read recently about newer engines that will include a humidity sensor so the ECU knows the humidity of the intake air. Now I understand how the humidity level of intake air affects combustion, but don't knock sensors and other existing technology already essentially cover this ground?
