FYI, here’s a handy post (from Nov 2011, but new to me today) on Windows 8 and Power Management of Metro style apps.
This works the same whether you are in front of the PC using it or leave the PC long enough for the screen saver or lock screen to kick in. Suspension of inactive apps only applies to Metro style apps, not to basic OS functions like copying files.
The post also talks about how running metro apps that are not currently being used can be closed to free memory.
Filed under: Windows 8