Anger and control

CMU researchers found that recollections of anger or fear could bias a person's outlook with regard to the likelihood of future attacks and coping with terrorism.

Each time, they created experiences that accentuated one of the multiple emotions that the attacks evoked: fear, anger or sadness. One year out, the respondents' emotional reactions to the attacks continued to predict their perception of the risk of terrorism: Those who had their fear heightened were more pessimistic about the likelihood of future attacks and coping with the risk of terrorism, while those who had their anger heightened were more optimistic.

The use of anger or fear seems analogous to a fight or flight response. Interestingly, sadness was neutral in impact.

Anger is sometimes adaptive, sometimes not:

Anger is probably beneficial in this context because it increases people's sense of control, comments Lerner, who also has looked at this aspect of the phenomenon...
"At the same time anger effectively provides a sense of certainty and prepares people for action," she says, "it also simplifies their judgment processes and leaves them prone to bias."

This illusion of control (it is, after all, contextual whether or not the sense of control is validated) has potential psychological benefits. Cf. this 1996 press release on optimistic bias in children:

Capps has found that normal healthy children have an optimistic bias in believing they will be protected from harm that others encounter. They think they have all kinds of control over negative events in life, rating themselves as less likely to be affected by danger than the "typical kid," she said.
"It's important for parents to provide this illusory faith," said Capps. "It gives an extra buffer against fear, anxiety and depression."

Anger can thus be a psychologically adaptive means of coping with lack of control, altering one's perception. However, that benefit is distinct from how adaptive it is with regard to more objectively bettering one's situation.