Both repaints and relayouts are improved, actually. The faster repaints are what improves scrolling performance (repaints are triggered every time you scroll, but relayouts are not) -- but because there are fewer elements in the DOM tree, relayouts are cheaper as well.
We experimented with using display:none instead of removing the elements; it increased scrolling performance just as much as actual element removal, but the relayouts when new content was appended got to be prohibitively expensive once a certain amount of content was loaded (literally pausing the browser for a noticeable amount of time), because the browser still had to traverse a giant tree of HTML entities during the relayout. So even if the buffer flip times are still too slow for you to get completely smooth scrolling in complex demos like this -- and that makes sense, given your large-screen setup -- you'll hopefully still benefit some from the faster, non-browser-freezing relayouts.
Both repaints and relayouts are improved, actually.
When actually is defined as for some on certain machines, judging from the number of directly contradictory observations in this thread.
The word "actually" ought to be reserved for concrete facts with zero counter examples.
The word "hopefully" in your closing sentence seems more apt.
That said, very much appreciate the sharing of the hypothesis and implementation. It's great to see ideas from other areas (video game terrain feature pop in) leveraged to improve end users' browsing experience.
We experimented with using display:none instead of removing the elements; it increased scrolling performance just as much as actual element removal, but the relayouts when new content was appended got to be prohibitively expensive once a certain amount of content was loaded (literally pausing the browser for a noticeable amount of time), because the browser still had to traverse a giant tree of HTML entities during the relayout. So even if the buffer flip times are still too slow for you to get completely smooth scrolling in complex demos like this -- and that makes sense, given your large-screen setup -- you'll hopefully still benefit some from the faster, non-browser-freezing relayouts.