So recalculating the virtual DOM is fast, but it does have a cost. The easy way to combat this cost is to realize that if you're doing things right and using pure functions, you'll get the exact same UI if you're state hasn't changed. So if you know the state that feeds into a certain component hasn't changed, you can get much better performance.

This library basically encourages you to use React's "PureComponent", which automatically does that calculation to see if the props have changed for you, thus giving you a huge speedup since only the components that need to update will.