Some games do it automatically (Path Of Exile), some give you the option (Grim Dawn, Civilization VI) to set a framerate limit while it is in the background - making the game preserve your resources when it is not needed. But there are many games which don't allow this, and they are running full speed while in the background even when paused. For those games it would be great to set a max framerate (like 1) automatically when they are in the background. I tried, setting manually works, but an automatic change would be really great: this would not only keep your PC quiet, but lower your bills, and increase the lifetime of your hardware. It also gives more resources to other apps while multitasking.