[rtomanek]

To add context: this is especially true for tasks that are likely to end in the device sleeping again. Two examples: user checking phone after hearing a notification sound or opening the laptop lid to check train departure time in the browser (then closing it again).

The faster the CPU deals with the task once the device is fully awake the shorter the time other power hungry parts of the system (like screen) need to be awake.

That's why slow phones, where the user needs to wait for their browser to finish loading the page will never be battery effective.