To Blog or not to blog

I am new to this blogging thingo and as yet I am not convinced it has a great deal of use except as a time waster. It is a little like the person in real life who likes the sound of his or her own voice and talks incessantly about themselves only this method reaches a larger audience. I can see the practical use for dissemination of ideas but often it appears a bit self indulgent. I'd be interested to hear of others opinions for and against.