I was indeed referring to the clouds shadow on the ground, as I noticed that when they show up in the field of view, the game stutters a little. Not terrible, but definitely noticeable, especially over trees.
Turning off shadows turns off shadows created by light sources (such as braziers, torches, etc). These shadows do place a demand on the GPU. Shadows cast by clouds do not; what you’re seeing is the visual effect of movement of the clouds over the trees (for example), not anything that affects performance. So turning off cloud shadows would have no impact.
@brad , thank you for your response. Where I do see the impact, however, is when the shadows cast by clouds go from the ground to the top of trees and back to the ground. If I go over a fairly dense tree area (but still with space between them), when the pixel of cloud goes from cloud to the top of the leaves on the tree, or from the top to the ground, there is definitely an impact that can be seen, especially when heartlings are running around in the same area.