Using "as:" gives a name to the route so you can refer to it like play_narrative_path with a helper.
If the path contains a symbol (:id), then you can pass it as play_narrative_path(symbol_here).
It's not necessary if you don't plan to use the named path (I don't think it's used as the moment, but we can use it).
Read more: http://guides.rubyonrails.org/routing.html