Tags and categories which are treated the same way by search engines are not required for SEO purposes. Watch the Matt Cutts (Google) video here > http://onecoolsitebloggingtips.com/2012/03/01/revisiting-keywords-and-tags/ All search engine spiders use them for is to compare them to your text in posts. If the keyword in the tag is not in the text in post they suspect you are a tag spammer. Tags and Categories are for your visitors convenience. By clicking them they find every post assigned to the same category or tag in your blog.