My opinion is that anger is most useful when protecting someone or something you love. [MENTION=8584]SpankyMcFly[/MENTION] may have a story he wants to relate here. Although, I think in his case it was more instinctual than emotional, I feel like it comes from the same place.
I do agree that in a modern, highly connected world, where real threats are more accidental and structural in nature rather than intentional things coming from individuals (though there are still plenty of cases). The impulses of anger can be misplaced.
The times I have felt anger to be most useful is when I have had to defend my friends, or myself. It has been a long time since I have needed to use it in physical confrontation.
One other use, I think, is as a marker for ourselves. I believe, the things we get angry at are things we feel threaten what is important to us.
I have recently had a string of times when I have gotten angry in ways that surprised myself. Although, the results of me not controlling my temper were not good, I did find out a little bit more about what I valued and wanted to protect.
Edit: I definitely seem to get consistently irate when I perceive people are being picked on. My perceptions can be wrong, and I have a bit of a hair trigger on this. But it comes from someplace that is deeply ingrained in my experiences.