Why bother having an index future, does it provide any benefit.
Futures markets exist to offer a means of offsetting risk.
They provide the greatest plus of additional liquidity to the overall market place.
Look at the rise in trading volumes in the FTSE since the introduction of its future.
This has led, in turn, to much tighter spreads on share quotes.
As an example of managing risk, an investor might be nervous of the market over the near term, but positive over the long-term.
A short term sale would incur costs (spread, commission and also might incur a CGT liability.) One way of achieving a reduction in the risk is to sell the futures while maintaining his underlying positions.
On the other hand a investment manager might be aware of new money coming into his/her fund in the future, but is also nervous of missing a good buying point. A timely buy of the futures could cover that risk, which would be redeemed on the arrival of the money.