A small team of planetary scientists from the California Institute of Technology, Université Côte d'Azur and Southwest Research Institute reports possible new evidence of Planet 9. They have published their paper on the arXiv preprint server, and it has been accepted for publication in The Astrophysical Journal Letters.
The reason clocks use it, is to not make it look visually unbalanced. Most often they write 4 as IIII. I find it infuriating to break such a simple rule though.
But also, I’ve never ever seen VIIII.
Julius Caesar’s memoir of war in Gaul makes use of VIIII, for instance. You’re right that it’s much rarer, but was still used contemporarily and in modern times.