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.

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.