I agree.  You do it to decrease tax liability.  If you don't need it though you spent extra dollars to avoid paying taxes, which in reality is less money than what was spent to avoid the taxes.

Now matter how you slice it, it is spending X dollars to avoid spending Y dollars where X>Y.  Interesting, how some would rather give to the rich to blow how they like rather than to the government to blow how they like.  Guess it all depends on who you like to play with your money.