It’s hard to overestimate the importance of clouds in Landscape Photography. When I started out doing Landscape I thought blue skies were the best. I guess if you’re used to boring overcast clouds of whitish-grey, the saturation of a blue sky is really pleasing to the eye. However, artistically, it becomes a large space with nothing interesting to hold your attention.
If you’re shooting Macro, these clouds are just what you needed as they diffuse the light leaving no harsh shadows and good saturation. Usually with Macro photography we aren’t including the sky in the photo anyway.
On the other hand, not all Landscape photos need the sky. Take a look at the photo of Spiderock in my earlier blog post here. The overcast sky took away from the mood I wanted to portray, so I left it out. I had to clone in some dark grasses (in Photoshop) in a small strip at the top. (not shown)
Finally, here’s an example from my recent trip to Arizona. The site is called Church Rock. As great as Church Rock is, the clouds made the composition. I used Nikon’s super wide-angle lens Nikon 14-24mm f/2.8 to exaggerate the clouds.
More Info on Clouds
Wikipedia has a short article on clouds that might be helpful here.