There is basically a sprite per chunk, so think about it according to how many chunks you can see. That number is how many are processed on each tick. The default roughly covers a zoomed out view, so that all are updated. Smaller numbers create a queue/backlog, so perhaps the top left area is handled, then the bottom right on the next time. It's less about quality, and more about smooth changes. It shouldn't get jittery, more like reacting slower. The previous default was 10; since it's one of the "hardest" things that happens, it has the most impact on UPS, I think. That said, in my tests, it's all still quite fast. If you're tweaking for performance reasons, I'd like your input/results if you think it could help.
