This demo shows how you can build a "smart scroll" jQuery plugin that would start initializing the chart only when it scrolls into view.
Having many charts on the same page might essentially bog down the browser if they start initializing all at once. By having only visible charts initializing, we avoid this issue, resulting in way better UX.
You can also check out this demo, which uses alternate approach to lazy-loading, by overriding the makeChart function.