Advantages and disadvantages of counter flow in heat exchangers over parallel flow?Why counter flow is effective?

Advantages:

•   While the temperatures T (of the cooled fluid) and t (of the warmed fluid) in the parallel flow heat exchanger can only approach each other, they can pass each other in the counter flow (Tout < tout) and in this case there has to be more heat been transferred
• One other advantage for the counter flow, since the maximum temperature differences between the two flows are much smaller, they suffer less thermal forces.(Low thermal stresses will develop in counter flow as temperature difference is uniform throughout the length of the exchanger