Penelope Trunk has a post titled Blogging essential for a good career. She writes that a well-executed blog sets you apart as an expert in your field. Penelope lists eight reasons why, after deciding about topic, blogging helps your career.
1. Blogging creates a network.
2. Blogging can get you a job.
3. Blogging is great training.
4. Blogging helps you move up quickly.
5. Blogging makes self-employment easier.
6. Blogging provides more opportunities.
7. Blogging could be your big break.
8. Blogging makes the world a better place.

In another post, Benefit from blogging without spending tons of time, Penelope adds some more tips.
1. You will force yourself to specialize.
2. You will let people know you have good ideas.
3. You will show passion and commitment.