I personally do it just before scrolling. I'll highlight a few lines of text 2/3 down the page, then scroll until it's right at the top of the page. It's an eas

I personally do it just before scrolling. I'll highlight a few lines of text 2/3 down the page, then scroll until it's right at the top of the page. It's an easy way to avoid losing my place. I've also seen people who use the highlighted block to follow their gaze, though I can't speak to the logic behind that.