The other day I ran into a great discussion on David Gurteen's website of a blog post by Nancy M. Dixon together with a video, where she talks about that fact that one also learns when one talks. It immediately reminded me on the learning process that happens when I write (s.a. How do I know what I am saying until I see what I wrote).
The idea behind both is that sharing (be it in writing or talk), has strong learning elements, because you need to formulate your ideas to be conveyed. This has happened to me quite often also when presenting similar talks multiple times. It does not become boring, but it can actually lead to additional learning each time one gives the talk.
We often tend to see the recipient of a talk or a written piece as the only one that learns, and hence think that sharing knowledge is a one way transfer of value, while indeed the direction of learning might be the other way. For example through smart questions that trigger new ideas or through getting clearer with an existing idea or thought while formulating it for other's consumption.
Keep that in mind the next time somebody has this "Knowledge is Power" attitude, they might actually be cutting themselves off some valuable insights and learning.