As the first presidential election of the post-Citizens United era, the 2012 campaign was expected to be a Caligula-like orgy of political spending, one long advertising binge fueled by Super PACs capable of accepting unlimited donations from the nation's concerned billionaires. And guess what: it was! The Center for Responsive Politics guesses that the final tab for all federal elections this cycle will total $6 billion, topping the 2008 total by $700 million. More than a million ads aired for the presidential campaigns alone through October 29, a roughly 40 percent leap from 2008 and 2004.

In the course of this election, though, we've learned something interesting about Super PACs. While they're capable of funneling lots of money into the political system, they're also incredibly inefficient at it. And, as the Wesleyan Media Project noted in a recent report, that explains why the Obama campaign and its Democratic allies have managed to buy more ad spots than Romney and his GOP supporters, even while being outspent.

When it comes to TV advertising, Super Pacs are at a disadvantage thanks to a law that requires stations to charge political candidates their lowest available rate for air time -- what's known as the lowest unit charge. Here's how attorney David Oxenford explained it on his Broadcast Law Blog:

Essentially, lowest unit charges guarantee that, in the 45 days before a primary and the 60 days before a general election, candidates get the lowest rate in any class of advertising time for a spot in that class that is then running on the station. Candidates get the benefit of all volume discounts without having to buy in volume - i.e. the candidate gets the same rate for buying one spot as your most favored advertiser gets for buying hundreds of spots of the same class.

Super PACs don't get that discount. Instead, they have to pay full market value for their ads. And so, while the Obama and Romney campaigns spent less than $560 per commercial from April through Ocotober, the Koch brothers-backed Americans for Prosperity and Karl Rove-run American Crossroads both had to shell out more than $800.

That difference has weighed heavily in Obama's favor. Of the more than 570,000 pro-Obama ads that ran from April through October, 88 percent were sponsored by the president's campaign. By contrast, 51 percent of the pro-Romney ads during that time were aired by outside groups. And so while the GOP nominee and his top supporters spent 18 percent more than Obama and Democratic groups, they still trailed them by just under 50,000 ads.