This leisure keynote by Richard Dawkins offers a most impressive defense for the use of social activity that would otherwise be deemed useless.
Dawkins agrees that things like poetry and belly dancing are difficult to make a case for as useful contributors for human survival. But he feels that the brain that is capable of participating in such will not only be able to perform other tasks, but will also attract the opposite sex.
His leisure keynote brings up a sexual choice theory in which is exemplified by the mind being the equivalent to a peacock's tail. Potential mates think "clever is sexy" and those with big brains can "remember epic poetry" to impress them.