The recent theory by Hugo Mercier and Dan Sperber about how human reasoning evolved for the purpose of argument uses as evidence findings that people get more reasonable when they argue. In other words, we reason better when we are trying to persuade. I am sure that is not a general rule, but when I read a good point-counterpoint I am struck by how much I can learn -- not just by a journalist saying "he says-she says" but a real back and forth, with supporting evidence from each side, not limited to what will fit in a 1000 word newspaper piece, as interpreted by a generalist.
"we reason better when we are trying to persuade." I conduct as well as teach legal analysis and writing, which means I think about persuasion somewhat regularly. This principle should be boiled down further to the blindingly obvious:
We reason better when we are forced to.
(When are you forced to explain why you think what you think, or, often, what your gut tells you to think? Well, among other things, when you have to convince someone else that what you think is RIGHT. That is, persuade them.)
We reason better when we make ourselves reason, rather than simply "know".