The software side of the power equation is getting some additional attention in Mountain Lion. In previous versions of OS X, the OS would wait for at least one minute of disk inactivity before putting the system to sleep. This decision could be vetoed at the last moment by any application that preferred the system to stay awake.

This strategy of having the system timidly request a reduced power mode after a polite interval is far from optimal. What if the application that canceled the sleep request will be done with its work in another 10 seconds? The OS will still wait for another whole minute of disk inactivity before even attempting to put the system to sleep again.

In Mountain Lion, OS X no longer pays attention to disk activity when deciding if it's OK to put the system to sleep. Instead, Apple recommends that applications make what Apple calls "power assertions" as a way to tell the OS when they're doing some useful work that the system should stay awake for. This policy allows the OS to put the system to sleep the moment there are no applications still holding power assertions to prevent the action.