What I'm interested in is not the advantages of this approach, as this seems to be the preffered approach today and its pros have been discussed on this site.
I'm interested in the advantages of the more traditional, backend-based approach. Where the templating and routing of pages happens on the backend, and the frontend logic is thin.
Please note, that this question refers to standard 'CRUD' applications, not to specialized video-editing software or programs executing intense algorithms (this kind of computation obviously needs to happen on the backend).
I'm referring to the advantages of a backend architecture for your 'typical web app'.