[tmcneal]

Along those same lines, I'd bet that the floating section was added to get more eyeballs looking on the right side of the screen where the ads are.

[rhizome]

I'd say that along those lines, one aspect of the purpose of the sections is that the center is long-form attention and the right sidebar is short-form "constant check" attention.

And just to put the button on it: I fully believe that FB is at least this cynical when it comes to the design of the page.