"Blueprints" are designs for ambitious, extensive development undertakings that are too large to fit into any one Idea or Ticket.  A blueprint card should be created when and only when there has already been substantial design work, and all related tickets should be tagged with the blueprint's name.

Blueprints are not  to be used as placeholders or mere tags, and are not intended to unify a bunch of loosely related functionality; they are for managing major feature implementations, deep refactorings, and other undertakings involving significant dependency chains.