You can throne room/KC/Procession a Monument; TR/Monument is a reasonable alternative to Throne Room/Butcher when you have only 1 curse in hand, and KC/Monument probably is superior to KC/Butcher in that circumstance--though of course the kingdom and the stage of the game would determine whether you want more VP or coin tokens.
More exotically: if your deck consists of KC/Scheme/Bishop/Platinum/Platinum/Colony/curse and your opponent has Mountebank or Masquerade, you would want to keep the curse to defend yourself against their attacks. In that case, if you had to buy an extra card, you'd prefer to have Monument than Butcher. (Granted, I'm not sure why you'd want either card in such a scenario, but we're edge-casing here.)