When pipeline caching is enabled, VisIt tries to retain all of the geometric primitives that are used to draw a plot. This greatly speeds up animations once the geometry for all time states is cached. The downside to pipeline caching is that it can consume large amounts of memory. Pipeline caching is enabled by default, but sometimes it makes sense to turn it off. The deciding factors are the size of the database, the number of animation frames, and the number of plots in each animation frame. Try leaving pipeline caching enabled until you notice performance degradation. To turn off pipeline caching, uncheck the Pipeline caching check box in the Animation Window.