This is so easy and I, a software developer with no actual experience in that area, know the obvious solution that eludes that hundreds of developers with actual experience in the area. Meanwhile, I take umbrage when my product manager tells me that implementing the next feature will be easy and I'm exaggerating how complicated it is."
if (not_visible) { suspend_wait_and_stop_consuming_resources }
I can imagine that it gets massively more complicated. However, as, say, an executive, this probably indicates that you can lean on your sw dev staff to approach the asymptotic ideal that looks so simple if you really care about the goal.
[1] E.g. Firefox added some in version 58: https://developer.mozilla.org/en-US/docs/Web/API/Page_Visibi...
Well, the difficult part is not writing an if statement...