Facebook's Heavy Investment is Worth it

Facebook deserves the benefit of the doubt about its rocketing costs. The social network’s bills jumped about 80 percent in the fourth quarter. That’s worrying - it’s twice as much as the top line grew. But all-important mobile advertising revenue doubled in 90 days. The potential profit justifies heavy investment. The proliferation of small screens was the biggest threat facing Facebook. But there increasingly are signs that it is turning this into an even bigger opportunity. Advertisers had been reluctant to promote their wares or services on tablets and smartphones. And Facebook didn’t even bother trying to entice them until last spring. But increasingly slick mobile devices and better metrics for measuring the effectiveness of campaigns - and the fact that people now spend so much time on their devices - is attracting advertisers. Facebook, along with Google, appears to be on...