We're hearing of another new feature Microsoft is working on rolling into Windows 8 with the primary objective being to extend battery life further while also improving the OS' performance – App Suspension.
Essentially it's an optimization within the kernel whereby any applications currently running in the background that show very little activity would be frozen (or suspended) so that they no longer use any CPU cycles at all, thus helping out in terms of power consumption (giving better battery life), or freeing those cycles up for other more active applications at the time.
It certainly sounds like it could be a useful attribute in the case of Windows 8 in particular where a fair number of Metro applets would likely be active in the background and are seldom called upon. It would also be of benefit to gamers in the performance dept, helping free up resources by automatically suspending unneeded processes during your gaming sessions.
KitGuru says: Providing MS gets it right and it doesn't result in crashes and other instabilities, this can only be considered a useful implementation.