On the other hand if you have a blog with content that's being updated daily, or every few days then you're giving them a way to interact with your content. With a blog they are able to post comments and tell you how they feel about the content you have posted. You can even allow people to post to your blog. This type of interaction creates loyal readers. Especially if you're content is good. And loyal readers come back.
The number one priority for your blog is content. Because, lets face it, if your content sucks then people aren't going be interested in reading it. Let alone come back for more. You don't have to have super great content either. Believe me when I say that it's OK if you're not a great writer. Not everyone who owns a blog is a great (or even good) writer. It's far more important if you are able to produce content that's helpful and informative, and stands out, and then people will come back for more. Simply put yourself in your readers place. When was the last time you visited a blog to read the ads?
I've seen a lot of blogs that have really great content that I've wanted to comment on but couldn't. I never went back. People don't want blogs they can just read, they want blogs they can interact with. Preventing people from commenting on your blog is something you should never do. Always leave your comments on. Readers want to tell you what they think. You need to let your readers write back and speak their mind. And take my word for it; people are not always going to agree with what you have to say. If you're worried about spam there's no need to be. There are free plugins you can download that will help prevent that.
As your blog grows and more people read your blog you might want to consider allowing your readers to write posts for your blog. This is called guest posting, or guest blogging. Either way it's a great way to inspire reader loyalty. Just make sure you set up some rules, and each post is approved by you before it's posted. You can also do the same thing on other blogs. Simply email the blog owner and ask if you can submit a post. Not only will this give you a link back to your blog (which is great for search engine ranking) but you can also direct more readers to your blog.