Researchers from the University of New South Wales in Sydney, Australia found that people who are sad have better memories, improved judgement, and better thinking and communication skills than people in happier moods.
One of their experiments took volunteers who were in different moods and tested their memories of a staged purse snatching. The eyewitness accounts of people who were in a bad mood were more accurate than those of people in a happy mood.
The study's lead author, Joseph Forgas, says this shows that a positive mood is likely to make our thinking less careful.
In another experiment, volunteers were asked to write down an argument in favor of a particular proposition. The results were analyzed for quality and persuasiveness. And the researchers found that people in a negative mood when they wrote the essay were more effective in their critical thinking and wrote more convincing arguments.
Forgas says the findings support the idea that bad moods and negative emotions help us deal with threatening situations.
When you're in a bad mood, you pay more attention to detail and you process information better   more critically. But when you're in a good mood, you feel safe, not threatened, and you're not as cautious.
So if you get your purse snatched and you need an eyewitness, pick the bystander in a bad mood. They'll be better able to identify the thief.