What are the tradeoffs of using a heavier server side template engine like Blade or Twig compared to building a fully client side rendered frontend using a JavaScript framework consuming a PHP API?

A server side template engine like Blade or Twig renders complete HTML pages directly on the server, which tends to produce a simpler overall architecture, faster initial page loads since the browser receives ready to display HTML immediately, and generally stronger default search engine visibility, whereas a fully client side rendered frontend built with a JavaScript framework consuming data from a PHP API offers a potentially richer, more interactive user experience with more granular control over client side state, at the cost of additional architectural complexity and typically a slower time to initial meaningful content on the very first page load.

// Server rendered: PHP outputs complete HTML directly
// Client rendered: PHP only returns JSON, JavaScript builds the HTML
return response()->json(['products' => $products]);