Olaf Brugman at his Goiaba Knowledge Bridge says Knowledge Sharing is Paying Tribute:
To share knowledge with others is a form of paying tribute to those [who] once shared with us, and who helped you become what we are now. As such, knowledge sharing is a quite rewarding experience. Read on to learn why.
Olaf runs through several reasons why knowledge sharing is important, regardless of what you call it. I think he hits a very important point when he says that the act of sharing with one another is the reward in itself. It is a central human activity that is difficult to quantify. You share with me what you learned from someone else. Then I take what you've given me, combine it with what others have taught, and pass it along to other people. By this I develop my own understanding as well as passing on important information to those other people.