Do you treat the IRS as you own personal piggy bank? If you do you are loosing money, do you like loaning your money to people for free. If you reduced your tax liability and put the money in a savings account you could be earning money instead of loosing it. The IRS only want's what is owed, so why give them more than that?
Think about it, when you borrow money from the bank, do they do it for free?
Why should you?
Just something to think about.