When you change the state of a React container, it will re-render its children, who re-render their children, and so on. In Flux terminology, this is called an update round. From the time state changes to the time that the UI elements reflect this change, this is the boundary of the round. It's nice to be able to group the dynamic parts of application behavior into larger chunks like this because it's easier to reason about cause and effect.

A potential problem with React container components is that they can interweave with one another and render in a non-deterministic order. For example, what if some API call completes and causes a state update to happen before the rendering has completed in another update round? ...