It's not the payload size that matters really, but the latency of requests which you have to wait between interactions, making the UX synchronous and slow. Goo

It's not the payload size that matters really, but the latency of requests which you have to wait between interactions, making the UX synchronous and slow. Good examples are, well, almost any modern and popular app. Like Trello for example. Users spend lots of time on the same page making micro-interactions, creating cards, moving cards around, adding tags, etc. You want to make the in-app experience as flawless as possible in these types of apps, and the initial JS size doesn't matter so much especially when it's cached. There's also lots of shared state and you might be saving multiple things on the server at the same time or uploading multiple files in the background while editing other parts. You might want to store data offline and sync later to the server. Once you have decent complexity, JS app with framework such as React help a lot.