But then if you switch windows or tabs, the timer for the animations in the tab that is now invisible can be stopped, surely?? Why redraw an invisible window?

But then if you switch windows or tabs, the timer for the animations in the tab that is now invisible can be stopped, surely?? Why redraw an invisible window? In any ordinary paint routine, you query for the invalidated rectangle and only redraw what you must. In the case of pages that are out of view, then nothing needs redrawing. Processes that are busy doing things they need not (like redrawing on a timer, polling a mouse) is why Apple starting highlighting offenders in macOS (what is hogging the battery??) and why I don't use Chrome on it - it just gobbles power keeping all of those tabs alive. Hopefully these new changes will help.