Nothing is forcing you to put everything in Redux. If state only has relevance to a single component then keep it in that components state, Redux works perfectly fine with this approach.

You have information which has global nature, used in multiple sorts of the application. This could be, among other things - STDIN/STDOUT/STDERR file handles - static configuration - some parts of runtime configuration - application info (in a game maybe current score, current level, active players, ...)

All that information exists only once and is needed in many parts.

Like the state of the logged-in user.

I think these debates about global variables or state could be much more specific, though.

For example, we tend to realize that letting any component access a `require('./store').currentUser` singleton may make testing harder, but this global dependency still exists when, say, it's distributed to all components through the React context. I reckon most people are thinking of the singleton example when they lambast Redux but it certainly doesn't have to be that way.