There are two compelling reasons to write tags for your blog posts: You want to make nice with search engines (SEO), or you want to make friends with your blog’s visitors.
Blogs excel at easy-to-understand navigation. On a blog landing page you’ll usually see a set of categories, like breakfast, lunch and dinner on a recipe site. Underneath this first layer, the blog writer defines a much more granular navigation through the use of tags. Blog tags link stories on similar topics together. For example, a story about eggs benedict might contain the following tags: eggs benedict (leading to additional eggs benedict recipes), eggs (leading to all egg recipes), and high cholesterol. You get the picture.
This tagging system helps the user find similar articles of interest and explore your blog; and, behind the scenes, it allows search engines to catalog the most unique and deep content on your blog.
The quick advice is: don’t post without tagging. Aside from search or tedious “drilling down,” it could be the only way readers will find your valuable content.
For more information, check out categories vs. tags and using tags to benefit your readers and SEO.