A catchphrase can be a double edged sword. Good ones can make a character more memorable. What would characters like Judge Dredd ("I am the law!"), Optimus Prime ("Transform and roll out!"), and Batman ("I'm Batman!") be like without their iconic lines? On the other hand, a bad, out of place, or overused catchphrase can make a character ten times more annoying than they would have been otherwise.
What makes the difference between a good catchphrase and a bad one? What kind of characters work best with catchphrases and what's a good general rule on how often to use them?