Not the parent commenter, but I believe the idea is that if the webpage uses a framework like React or Angular, then the server doesn't need to send html, it ca

Not the parent commenter, but I believe the idea is that if the webpage uses a framework like React or Angular, then the server doesn't need to send html, it can just send the bare minimum data necessary (in JSON) and the client turns it into html and displays it. In other words, HTML is just the standard format that the browser uses. But if you use frameworks or define your own application specific formats, you can send less information over the wire and have it properly decoded and displayed by your client-side javascript.