Tags cluster liked themed topics together making them easier to find. It is similar to how relay affiliation assists automatic relay selection by reducing the set of candidate relays a client is to search through and choose from; similarly, the potential for tags can help to reduce search results. Additionally, they help to provide a vertical thread or path of knowledge in which customers can follow to see and stumble across related posts.
Some use cases:
Tag all posts in which a client behavior is the central theme in the topic. For example “client-relay selection”
Tag all posts in which the post involves the publishing of a custom web report “custom report”
Tag all posts in the Release Announcements category in which the release announcement pertain to the Patches for Windows site, or the WebUI, or SCM_PCIDSS, etc.