Why read a guest blogger?

Many blogs use a guest blogger from time to time, some use guest bloggers all the time; in fact, Matt Coddington suggest that just about every blog will include a guest blogger at some point in its lifetime.

A guest blogger simply means someone else writes a post or series of posts that are published on another blog. For example, I have done some guest blog posts at The Study Gurus. Sometimes it is one or two posts, sometimes there are many posts in quick succession and sometimes a number of guest posts are added over a longer period.

As a reader of a blog, why would you read a guest blogger in a favourite blog? Or would you actively not read it at all?