Why do animals have tails?

Animals have tails for assisting in balance and steering, propulsion,
grasping, grooming (swatting flies is one example) and for display. One of
the gaudiest tail displays I can think of is the male peacock's tail. Believe
it or not, we still have remnants of tails because or ancestors did. This is
a good example of a useful characteristic (the tail) evolving in our ancestors
but not being retained in the descendants (us!) because of a loss of evolutionary
selective pressure. Because we can modify our environment, it is unlikely that
we will evolve to regain tails! What other uses for tails can you think of?