pete,
my thoughts on this were simply that the water heats the throttle body just around the butterfly, and prevents icing/frosting of the t/b when driving around and near closed throttle (who drives like that!!??) ie: high velocity air around the butterfly.
no idea if this is true though.
i disconnected mine for a while as the damn pipes had rusted, and found zero difference. does make the engine look neater though.