Some bloggers have been able to generate massive amounts of traffic by regularly writing guest blog posts for other blogs. Have no idea what’s guest blog posting? It means writing blog posts for other blog publishers rather than for your own blog. It doesn’t mean you stop posting on your blog and just write for other blogs (it’s another matter if you get paid for this). A good mix can be, if you write 5 blog posts every week and you cannot simply squeeze in more time, you can use to blog posts as guest posts and remaining three for your own.
Besides creating diversity, as mentioned by Chris in this guest blog post, guest blogging also gets you high-quality in-coming links. More people begin to know you because your profile routinely appears at various places. Once people know you and recognize you and value your writing they also start promoting your links on various social networking websites like FaceBook and Twitter: it becomes sort of a cascading effect.
Another benefit of guest posting is that people start showing interest in guest posting for your own blog. This way you can devote more time on promotion.
Here is a different thinking of the site. I think it's good.
Good call on highlighting promotion for the guest posts that you get live. It shows the webmaster that you actually care. Then, maybe you’ll be able to become a regular contributor!