Why is React's concept of Virtual DOM said to be more performant than dirty model checking?

I saw a React dev talk at (Pete Hunt: React: Rethinking best practices -- JSConf EU 2013) and the speaker mentioned that dirty-checking of the model can be slow. But isn't calculating the diff between virtual DOMs actually even less performant since the virtual DOM, in most of the cases, should be bigger than model? I really like the potential power of the Virtual DOM (especially server-side rende

[koba04]

good question & answers