[allover]

Being able to do so is certainly a cool feature. But I've built a lot of apps prior to Redux and never felt like state replays were a must for debugging.

There are various ways to debug state in a React app that uses setState. React devtools show each component's state, and you can combine that with breakpoint debugging as per to figure out how you got there.

[eropple]

Yeah, you can use breakpoints, but...that's awful. Like, it feels like crap to do, you end up stuck in half-transactions and other nonsense because you have no better options. The use of Redux (or any other functionally-oriented action-based state system, I was writing them in Java and C# long before I ever used Redux) enables powerful stuff that, yeah, might not be a "must"--but being a "must" and being a transformatively powerful tool that requires very little cognitive overhead to leverage aren't that far off.