How complexity affects macroeconomics and results in calculation problems in ergodic (deterministic) models due to emergence in that a whole (system) is greater than the sum of its parts (elements) since unforeseeable properties may arise from the relations among the elements. This is true even in the physical sciences and even more so in the life and social sciences. It's one reason for radical uncertainty and a strong argument against a neoclassical approach.
Bubbles and Busts
Macroeconomics Could Benefit From Complexity