I meant beneficial when you use it on yourself...
That's kind of situational, but I could see Downgrading an Antimattered creature so it stops healing and starts doing damage again, or a low health Elite Armagio to essentially revive it.
I just thought of something: what would happen if you Downgraded/Upgraded a Chimera? Instant kill, since Chimera's base stats are 0/0? Or would the new Chimera be re-played, absorbing all creatures on its side (minus its previous self)?