I’ve yet to build a Vue app that I felt needed external state management (though admittedly none are huge SPAs) but I have felt the pain in React working on a similar sized project. Just something about how the events work out of the box. React I felt like I needed to pass in functions to change parent state through a callback function in props, whereas in Vue I just emit the event and forget about it.

You can still use the function prop pattern in Vue but it doesn’t make much sense when event emission is so much simpler to reason about.

I purposefully avoid Vuex until a) the state becomes large or b) deeply nested objects (which reacitivity handles poorly, as whole trees rerender) or c) when I have lots of deep nested Components with a maze of events.

This is where I've found Vuex is a life saver for reducing complexity, organizing state in a seperate area, and having a consistent interface for accessing/mutating data without a tangled web of events and functions across multiple files/layers.