All the above posts cast interesting and truthful views as to the importance of history.
I'd like to add that a knowledge of history informs the present. Regardless of whether we can learn from past mistakes, since man is said to be the only animal who stumbles twice on the same stone, history helps us understand the world in which we live "as is."
If we take an active interest in evolution, many of the things we take for granted will acquire a new meaning. Some people contend that, as history is past -or so they think- it is also dead.
It would be wise to conceive of history both synchronically and diachronically. A synchronic view tells us of what was happening in the world at the same time. This shows us the diffences and similarities among cultures at every step of their development. A diachronic view shows us the links in the chains of events that have led mankind to its present state.
We generally like to know about our family history. In the big picture, History as a discipline explains the whys and wherefores of that extended family we call the human race.