First of all, you don't get it "back" you overpaid. Yes I am getting a refund, but you know what, since the United States is going to shit, we are in debt, we don't produce anything anymore, the United States is going to crash economically and militarily. I will have to readjust my earnings, because next year, you just might not get a refund, if the government is broke and they can no longer cease to pay out, just look at some states not paying in a timely fashion their bills, because of the latest economic crisis.
If that was to happen on a federal scale, I would certainly not want to be overpaying the Government! Also the money I overpaid is not giving me ANY interest or benefit. If I could increase my savings by $5 a week instead of overpaying every week, it would help me.
Some like this lump sum payment every year, but it does come with a very real cost/risk.