A: It turns out that, at least in western culture where the studies have been conducted, that SWB (high levels of positive affect, in particular) produces good outcomes in many areas. For example:
1. Happy people on average have stronger immune systems, and there is some evidence that they live longer
2. Happy people are more creative, at least in the laboratory
3. Happy people are better citizens at work - they tend to help others more, skip work less, etc.
4. Happy people are more successful - they earn more income, have better marriages, get job interviews more, etc.
5. Happy people do better in social relationships. They are more sociable to begin with, and other people like them more. They seem to be more successful in leadership work positions.
6. Happy people are better able to cope with difficult situations.
7. Happy people like themselves and other people more, and others like them in return. They are also more helpful and altruistic, on average.
8. Judgment and decision making. It is in this realm that laboratory psychologists have given happy people a black eye. Those in a positive mood have been found in lab studies to use stereotypes more, to be less logical, and to be more biased in their judgments. The well-known "Depressive Realism" hypothesis suggests that depressed people are accurate, and happy people inaccurate, in their judgments.
Check out this guys site http://internal.psychology.illinois.edu/~ediener/faq.html#SWB