Guest posts are one of the best ways to get some traffic to a young blog. But it's a tricky balance. Any new readers that you have should see that it's your blog and not someone else's. If you decide to have guest posts, be sure to intersperse them with a healthy amount of posts you have written yourself.
So why even bother with guest posts? Two reasons:
As I mentioned before, it takes awhile before search engines will even start to take your blog seriously. Therefore, a guest post is a good way to spark natural traffic. Feature someone that works in your field/does similar things to what you do. But featuring that person, there is a good chance they will announce the guest post to their friends/followers. So the traffic goes from only people you know to people you know plus all the people the guest blogger knows.
The second reason to have guest posts is that it adds variety to you blog and it help you to pace your ideas. A blog that has consistent, weekly posts always looks more appealing than a blog that seems to randomly update once a month. If you are scheduling blog posts every week, a guest post is one more week where you don't have to think of a new thing to write about. So it's a really good option if you're struggling for content.
I'm going to repeat here that your blog should not be only guest posts. Unless the focus of your blog is feature other people all the time -and you should state this as the purpose of your blog- guest posts should just add variety. Most of the content should be yours if you want to attract a loyal following.