There are times, in video, where we want 30 fps – but that can result in jittery motion if the shutter speed is fast. We can either use a longer shutter speed (e.g. 1/30th of a second) to blur motion, or we could shoot at higher frame rates (60 fps).
The authors propose shooting subjects that have fast action in 60 fps but continuing to shoot slower moving subjects in 30 fps. In post production, the entire production can be rendered as 60 fps by doubling up the 30 fps frame.
They did their tests, by the way, for 3D video. 3D likes good detail and does not like lots of motion blur, complicated the decision: how to render detailed 3D without ending up with motion blur problems.
(Actually, the link is to a PAL world discussion where they do thinks in 25 or 50 fps. I translated to 30/60 fps for the North American audience. Also, I did some similar tests sort of along the lines of the authors, but was just playing around with 720p/60 for 3D and found the results were much better than I had expected. But that also may have depended on the inexpensive cameras I was using.)