In my opinion, writing and hosting a blog serves several purposes. One, to hone my writing chops. Two, to express my own ideas in my own way... because it's my own "house" online. Three, I've actually landed some fairly lucrative client opportunities because of my blog. Four, it gives me a "home base" content repository from which to draw other ideas, participate in other discussions etc...

There are others, but these are the main ones.