Employed in cases where an actor working on the film is deemed to have too much talent, the Orlando Bloom will provide a sufficiently poor performance to ensure that the overall talent in the film remains at an average levels.
In extreme cases is used in conjunction with a Keira Knightley for a multiplied effect.
"My that Johnny Depp sure makes a great pirate."
"Yes, perhaps a little too great... Better throw an Orlando Bloom into the scene just to make sure the film doesnt become too awesome."