Yes, with the present DVD image size, in order to stick to the 4GB limit for cloop KNOPPIX, we have to remove programs to make room for substantial additions. (In my case, R, VMware Workstation and Oracle XE are the most important ones.) Instead of doing this, which is getting harder and harder to achieve while still keeping functionality intact, using the ability to chain cloop files can be very useful. I think that the main reason it has not been exploited more, is that it is kind of "third level" extension: First, the persistent store caters for most needs, second, creating a new primary cloop image suffices for most of the rest. I'm rather doubtful as to the usefulness of implementing version upgrades this way. Even within one release, it quickly becomes an hassle to keep it upgraded, and I guess this will be even worse across versions.