Performance enhancements in niche situations

I hit on a couple things that were a bit surprising to me... not sure what I'm really asking here, other than if these things are documented somewhere. Also kinda just going with the flow where this seems to be the place to raise generic "issues" even if they're not bugs :) 1. keys can make things slower I had a bunch of items, and the only thing that changed was their x/y positions. adding a key with index made rendering slower. It's possible this is short-sighted though since it could very well change once that "layer" has more items changing above/below it, but I found it interesting. 2. rendering null makes a _huge_ difference I had two test cases - a full graphics pipeline vs. an essentially empty POJO renderer. The difference in speed didn't matter about the data or graphics, but rather about what was returned in the components `render()`. For DOM this doesn't work of course - but for custom renderers, when it's known that a certain type of element will be an edge node - doing the side effects in render() (or some other lifecycle) and then returning `null` is _significantly_ faster than even a straight functional component that returns a simple element (which does the same side effects). This makes sense, since react then has less branches to consider (even if those branches point to nothing other than simple objects).