Futures positions might be established for a variety of reasons.

Speculation

Futures are an obvious choice to advantage from correctly anticipating a directional market move. These highly liquid contracts can be easily established and unwound. For a very bullish view you would buy futures, closing out the trade by selling once the price has moved up to realise a profit. For a bearish view you would sell futures, closing out by buying once the price has moved down to realise a profit.

Hedging (insurance)

Since futures contracts effectively represent a certain exposure to the cash market at a future date, they can be used to offset the risks of holding a position in the underlying, acting as a "hedge" protecting the value of your holdings.

Tracking

The exposure represented through futures can also be utilised to "track" the performance of an underlying market without direct investment in it, therefore eliminating frictional costs and difficulties associated with building up an underlying position.

Tactical asset allocation

Futures can also be utilised where you want to gain short-term exposure to a particular market or product without having to commit the funds necessary to gain that exposure in the cash market.

To summarise, the key advantages of futures are:

• it is easy to open and close positions - the market is highly liquid  
• leverage - you can buy exposure to price movements in a large amount of a given underlying with a relatively small outlay             
• you can go "short" - you can sell a future with the intention of benefitting from a fall in price.