Animations work by moving graphics positionally and changing the size and other features of the object. All the other transformational image patches and programing patches are also available for employment.
As detailed earlier, one can combine protocols within the same composition, so it can be used as both a ScreenSaver and a Visualizer. So long as an appropriately protocolised copy of the composition is saved within the correct Composition Repository, then such a compositoon would be available both within iTunes to visualize audio and as a screensaver too. One cannot combine Image Filter protocol with any other type of protocol based composition although Graphics Animations based compositions can combine any other protocol than Image Filter.
There is a third location that acts as part of the Composition repository, which is /System/Library/Compositions - reserved for core system compositions, given that these are exploited by Finder and other default applications, it is advisable to leave these alone, although there is nothing to stop one examining these compositions and exploiting them either for all users , or just for oneself.
You just have to remember to save them outside of the System/Library/Compositions folder.