[gpderetta]

the optimization could be vaguely interesting if you are implementing a lisp (or some other list heavy language) and don't want to perform too aggressive non-local optimizations to optimize the layout of lists.

[twoodfin]

As I recall, at least one of the Lisp machine Lisps used a bit in the cons pair to declare if the cdr (tail element) was immediately following.

EDIT: https://en.wikipedia.org/wiki/CDR_coding