> CPU usage is happening after the page has visually finished loading all relevant content This can be very noticeable though, leading to sluggishness, stutter

> CPU usage is happening after the page has visually finished loading all relevant content This can be very noticeable though, leading to sluggishness, stuttering scrolling, slowing down other tasks, increasing fan noise on laptops. uBO in my anecdotal experience may almost make a bigger positive impact in this fashion than simply at the initial render.