Ideally federal and state income taxes would be paid to the penny and not a cent more each year when taxes are due.  
But many taxpayers find this impossible to achieve.  So usually a little more or a little less is taken out of paychecks or put aside in savings each year so either a refund or a payment is due.  
What do you do, purposely pay a little more than expected due each year so you will get a refund, or pay as little as possible so you'll have full use of your money all year?
Me?  I deduct a little more.  I don't want to owe, even if it means I theoretically lose interest on that extra withholding.