It's more overhead in the sense that mobx needs to walk all your store objects and check for changes, on top of what React does. Anyway that's fine if you really need that precision. I just useMemo at the 'hotspots' and that is enough. Remember also that if vdom diffing doesn't pick up a change, nothing is flushed out to the DOM, so whether an object is created or long-life doesn't matter in this sense.