This Week in Gnome #187 Triple Buffered Notifications | Triple Buffering Merged for Gnome 48

There's a back buffer run by the CPU where it can render another frame in the background and pass it to the GPU so it doesn't have to wait for the primary buffer every time, giving higher frame rates, and also makes odd frame rates work better so you aren't restricted to just 30/60 etc. Reduces tearing, but might introduce input lag where you're dragging a window but the cursor doesn't follow the drag.