Cory Doctorow’s My Blog, My Outboard Brain captures the essence of blogging:
Blogging gave my knowledge-grazing direction and reward. Writing a blog entry about a useful and/or interesting subject forces me to extract the salient features of the link into a two- or three-sentence elevator pitch to my readers, whose decision to follow a link is predicated on my ability to convey its interestingness to them. This exercise fixes the subjects in my head the same way that taking notes at a lecture does, putting them in reliable and easily-accessible mental registers.
Much of what Cory says applies to me also!