Tags: Use of relevant tags is important from the SEO perspective. It helps the search engine track your post based on the tags you use.
Popular Topics: Stay updated with new topics or popular topics on other blogs you follow.
Add your personality - If you are writing on a particular topic, there are a number of people who will be writing on the same topic. So you need to add that specialty to your blog to make it look different and to allow your readers to take away something that the others are not offering.