There are usually some concepts that are captured with a word,
where you later want to use a different word. For example, in my design, a user can create a Suggestion, where previously this was called a Proposal.

If you tag your "concept" words with a hash, then you can rename your concepts easily. If my card would read "The #User can add a #Proposal" then a rename from Proposal --> Suggestion would automatically update the text of this card (and all other cards where #Proposal was used).

This will of course also make it possible to filter your stories with a set of hash tags (e.g. see only stories that involve #Users and #Suggestions)