? about clouds

Thanks for the answer about AI traffic, now have a question about clouds......my mind wants to soak up knowledge today!!From what I see, when people modify cloud textures to increase fps, it is usually the Cumulus01.bmp that gets reduced. What are all the other cumulus(cumulus_broken.bmp, etc) used for. When do they come into play? Why are these still left at larger sizes, and not reduced also? Would it not help if all cloud texture sizes were reduced?Thanks!Rick