Great question!  In this case, .json is not needed at all.

JSON *is* generated by Rails in its scaffolding process.  In the process of developing Rails applications, it's frequently convenient for certain REST actions to provide HTML and JSON endpoints-- the first for full server-side loads, the second for jQuery/AJAX requests that will update server-side state without a page reload.

In the scope of this class, we won't deal with JSON at all, at least not in a context like this.