Final answer:
Adding motion blur in After Effects increases render time due to additional computations for every frame to simulate the natural blurring of moving objects.
Step-by-step explanation:
Having a motion blur in After Effects will increase your render time. This is because motion blur adds additional computations for every frame that is processed to simulate the blurring effect that would naturally occur when objects move quickly. The render engine must calculate the motion blur for each frame, which can significantly add to the complexity of the rendering process, especially for scenes with a lot of movement or a high frame rate.