At the very least, the CPB requires that the budget actually adds up mathematically, something that cannot be said of the things that politicians proclaim ("everyone will get tax breaks!! we will close the budget by removing inefficiencies!"). Even though the prediction is not perfect, a group of experts can still detect outright wrong and misleading policies. In the US if a politician says "the middle class will get tax breaks!" you don't know if that actually means anything since another take hike might totally negate a small tax break. Even though the CPB cannot predict the future accurately, it can verify such statements by adding up all the proposed tax hikes and breaks and premiums, and use its statistical model of which policies apply to the middle class population to come up with a number like "on average a middle class person will have €56.30 more per month".

For example, check out this graph, which breaks up the effects of the new government by income level: http://static3.volkskrant.nl/static/photo/2012/14/8/6/201211...

The idea that you would do better by listening to the words of politicians on TV, than a group of experts working on this full time who actually calculate the effects of all the proposed policies sounds preposterous to me.