Guest posting has a lot of advantages, even if it is a mutual agreement. They help increase your followers and help to spread the word about your blog. It also reduces the work load of the person on whose blog the guest postings are posted. It also helps build backlinks.
Here are a few question for you:
Have you guest posted on anyone's blog or do you plan to do it?
What is your opinion about guest postings? Are they helpful to promote a blog?
Reason: minor edit