Ask HN: When does the modern web stack help the most?

What's an example of a web application (preferably open source examples) or type of web application where you really really want things like React and Redux? Or broader SPA features like component-ization and state management on the client-side?

Background: I've taken a break from front-end engineering but I'm looking at front-end positions and need some re-convincing, myself on some of the bigger design questions.

In my own experience, with some distance, I'm thinking none of them needed Redux, however this one is low hanging fruit and un-controversial. Most components don't even seem to get re-used in my experience. They're just split up because mega-functions are bad for other reasons. The ones that _do_ tend to get re-used are so simple that I'm not sure if I really even care about 1-way data flow, time travel, and all the supposed benefits I received.

So tl;dr I'm looking for stark examples where you could say "this project would have had less success without (insert core modern SPA technique)"