Since the scripts, stylesheets etcetera do not need to share a common origin with the server-generated json and html, there is no reason for the paths to the static resources to be hardcoded relative to the dynamic resources. Advantages of a configurable "static origin" include flexibility (because you can move the static content without moving the server side) and performance (because you can put the static content on CDN and you can avoid unnecessarily sending cookie data on static data requests).
Since the scripts, stylesheets etcetera do not need to share a common origin with the server-generated json and html, there is no reason for the paths to the static resources to be hardcoded relative to the dynamic resources. Advantages of a configurable "static origin" include flexibility (because you can move the static content without moving the server side) and performance (because you can put the static content on CDN and you can avoid unnecessarily sending cookie data on static data requests).