Kore Nordmann:

This shape matters because the single biggest cost of the SPA model is that it duplicates the server. State lives twice, once in the database and once in the client store. Rendering logic lives twice, as templates on the server and components on the client. And between the two halves you must now build and version an API which exists only to feed your own frontend. For an application which is genuinely client-state-heavy, like a collaborative editor or a design tool, this duplication buys responsiveness you cannot get any other way, and it is worth every line. For a catalog with a search box it is pure overhead.