Hashtags are tags that categorise a post under a topic and make it discoverable to people following that topic. Their importance differs between networks and has declined over time – today, most of the reach is determined by the content itself, not by the number of tags. They make sense in three cases: for narrowly defined professional topics with an existing follower community, for local tags, and for a company's own branded hashtag, which serves to gather content around a campaign or event. It is worth using a few relevant ones rather than dozens of generic ones that merely clutter the post. It is useful to check what is already being published under a given tag, so that the brand does not end up in an inappropriate context.
See also: Social network as a search engine, Brand safety, Organic reach.
