Regarding state on the client, my general concern is connectivity with the server. If I have a flaky mobile connection, or if I have a really high RTT to the se

Regarding state on the client, my general concern is connectivity with the server. If I have a flaky mobile connection, or if I have a really high RTT to the server for any reason, then I don't want UI interactions to start failing or slowing down left and right. Indeed, a lot of the sluggishness I've experienced with others' websites has to do with excessive roundtrips for trivial tasks like clicking around. So I'd prefer to keep most UI state in the client, if nothing else. (Of course it's still quite possible to make excessive roundtrips with an SPA framework, but it naively seems like it's at least more controllable than if everything is rendered server-side.)