It sort of depends on whether the fact that you might act impulsively matters to the other party. This makes all the difference in nuclear war or so some strategists say... In customer service, an angry customer could do damage to PR or if they are a big client, could cut off the company unpredictably so it would force them to decide if they want you or not and if they do act quickly. It pays to understand the difference between these situations. Anger should be used selectively and only when it will be effective (and preferably when the other party deserves it).