The discussion on garbage collection of these vlists is noteworthy. The paper admits that their aggregation causes retention of garbage ("Large parts of the unused list structure may not be garbage collected."), and since they have heterogeneous sizes, fragmentation also. But, oh, that's totally okay, because all you have to do is make your collector copying to compact these things and you're good!

cons cells cause no fragmentation whatsoever (they can be placed in a dedicated cons heap in which everything is a cons of the same size), and an unreachable cons cell is always reclaimable.