Hover effects, you often want to respond to the user hoving their mouse somewhere, for instance showing a tooltip.
Battery/network saving, a site can pause animations or reduce update requests when the window is inactive.
I cant really think of a good use for this one these days, it was something browsers had in the 90s (not just readonly, websites could move your browser window where they wanted for a while). Maybe its kept for backwards compatibility.
Great showcase on how much data your browser is unnecessarily bleeding to every website out there that wants it.
Genuine, non-rhetorical questions: does anyone know why the hell your browser needs to tell the site
That explains it. Thank you and @[email protected] for the replies!
Some ideas: