- AC Ascension Island
- BV Bouvet Island
- CP Clipperton Island
- DG Diego Garcia
- EA Ceuta and Melilla
- HM Heard & McDonald Islands
- IC Canary Islands
- TA Tristan da Cunha
- XK Kosovo
It is extremely useful to be able to map all of them to at least one unique TZID, if nothing else than for testing. It does not hurt to have extra links in order to make that true.
But it is more than that. There are definitely people upset to see their timezone reported as being that of a city in a different country, simply because they happened to have the same rules. Most of the above have small populations, where one could argue that it doesn't matter much (and Kosovo is a special case).
* excluding: Unknown Region (ZZ), deprecated codes (like SU), macro regions (like North America)