Use case:
You need to manually fill in a citation template. There are six authors. T52407: TemplateData: Add a way to express dependencies between parameters promises to let you add |last1= and |first1= at the same time, but you'll still have to do that six times, one for each author.
Why not make it possible to say "Give me six of these"? (Hat tip to @ManosHacker for this idea.)