Good question! The correct use of tags is to help filter posts by certain subjects. For example, using the tag "sports" in a post related to sports will help other users using the search function, to find the content they are looking for. On Hive a lot of people forget about this and are only using tags to farm 2nd layer tokens. For this reason I prioritize tags that are related to my post subject, and in the end I will use just a few community tags like pob, pimp and tribes.