When you write a post for a different site, most of the men and women who visit that website will see what you've written. When it's well written and participating they'll read the whole post and see the writer box that gets included at the conclusion of each guest article. If they liked your post, they could then click one of those links you have included on your bio. And that is traffic which would not always have seen you in almost any other manner.
Additionally, if you're able to produce a dialogue by inviting folks to remark on your guest article, it is possible to boost traffic much more. Clients begin to create a connection with you throughout the remarks and need to find out more by clicking in your avatar that links to your website.