I think SO and pure documentation would serve two separate purposes. Sometimes documentation is better for something like an internal library API or related information. But on the other hand, sometimes having a an SO-like place where I can go look up a question related to a quick thing I'm trying to do would be useful. Say I don't remember the process to build the latest version of a Java package and upload it to an internal repository or something, it might be quicker to find a related quick Q&A type doc for that rather than digging into dense documentation on a variety of things.