Core Image Filters are just one of several image patches employable within Quartz Compositions. The main difference between a Core Image Filter and other patches that can change the look and feel of an image is that the Core Image Filter is programmable using GLSL Fragment and Vertex shaders. When called as a protocol from the Template menu one can create an Image Filter protocol composition.
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 a copy of the composition is saved within the appropriate Composition Repository, then such a composition would be available both within iTunes to visualize audio and as a screensaver too. One can combine other protocols within an Image Filter template derived composition. One cannot combine Image Filter protocol with any other composition based upon any other protocol.
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.