[grrowl]

React simply stores a /representation/ of what the DOM looks like (just the tree of nodes). When actually hitting the DOM, the browser recalculates styles, layout, and may preemptively calculate other things for speedier rendering. Additionally, it's a lot "heavier" so jumping through a node's children, children's children, etc. is much more expensive than plain nested objects. Therefore, it's most efficient to wait until the browser is actually about to render (requestAnimationFrame) and update only what is different in one go.

More specific details here: http://facebook.github.io/react/docs/reconciliation.html