For the state theres an obvious advantage, coins are a lot easier to use than raw gold so there's a benefit to the economy (assuming you can stop them being debased). So that's why emperor's did it.
But for your average oligarch it's mostly just propaganda (or maybe theres a coin shortage in their region).
harkat82 t1_ixm6pqw wrote
Reply to comment by luke_in_geneq in Coins study suggests ‘fake emperor’ was real, say scientists by IslandChillin
For the state theres an obvious advantage, coins are a lot easier to use than raw gold so there's a benefit to the economy (assuming you can stop them being debased). So that's why emperor's did it. But for your average oligarch it's mostly just propaganda (or maybe theres a coin shortage in their region).