Once enabled in settings, your device will enter Doze Mode in minutes (instead of hours stationary normally) after the screen goes off if not charging, to improve its power-saving efforts.
Doze mode is a new power saving mechanism introduced in Android 6.0. In this mode, background behaviors of all apps (except white-listed ones) are strictly prohibited, until next user interaction or charging. The device will also periodically (in hours) exit doze mode briefly.
This is not the complete solution for a better Doze, currently it still cannot keep your device rest in doze if you are carrying it around. It is expected to maximize the power-saving effect of the stock Doze mode. (UPDATE: This "interruption by motion" behavior can be completely prevented in the newest version 2.9 beta, see FAQ.1 for details) Also it may break some background functionality of your daily apps if they are not developed with Android Doze in mind.
When I'm moving around, the Aggressive Doze is not working?
Android system uses a low power "Significant Motion Sensor" to track movement and exits Doze Mode if significant movement is detected. Aggressive Doze will not try to enter Doze after that, to avoid constantly entering and exiting Doze. Since the stock Doze is designed for battery-saving in stationary state, Android still wants to keep your apps in sync with fresh state if you are carrying it around.
In the new version 2.9 beta, this "interruption by motion" behavior can be prevented completely if "DUMP" permission is granted manually via USB-connected computer.
This seems like a bad consequence of Android Doze Mode itself if too many apps are installed. Because Doze Mode effectively postpone all the background behaviors during the doze. The longer doze lasts, the more tasks to do when exiting. Consider greenifying more background-itchy apps to reduce the lag, because hibernation is still the essential solution for them.
Check whether there's a alarm clock in less than an hour, by looking for an alarm icon in the status bar. But the icon won't tell you the time of the alarm. You may click the DND tile in the quick launch panel to find out the actual time of the alarm (in the entry with "until next alarm"). This is because Android system refuses to enter doze mode if an scheduled alarm is in less than an hour.
Aggressive Doze in Greenify v2.8 should work on all devices with Android 6+, unless the Doze Mode is explicitly disabled by the ROM. If you are using a custom ROM made by community, ask the
ROM modder to enable this flag in the ROM: