This reduces wakelocks or browser redraws that can suck your battery dry from the evening to the morning, as pretty often happens with some parasitic processes running in the background you aren't even aware of. Does your phone support Doze, though? You might think that this is a trivial question to ask about a device that is on Marshmallow already, or running an Android 6.0-based custom ROM, but not so fast.
Google's own Doze requirements are pretty severe - first off, it doesn't let manufacturer tinker with, modify or shunt Doze altogether in their Android overlay interfaces like TouchWiz or HTC Sense. Furthermore, you need both the Significant Motion Detector (SMD) APIs and Google Cloud Messaging for Doze to work as Google intended it.
Since not all phones have the necessary motion sensors, or even the whole Google Play Services Framework installed on them, even if they are on a Marshmallow-based ROM, they might not support Doze, so there is no point in trying fruitlessly to activate it. Here's what you need to do if you want to see if your device supports Doze in its entirety.
1. Download the Check Doze app APK file from XDA-Devs' ISDP member, and install it on your Android-powered gear;
2. Run the app, and see how many of the Doze requirements your device meets;
3. If you have the holy trinity of sensor support, Google Play Service framework, and the Doze configuration flag on, then you will be able to take advantage of Doze if and when it hits your handset. If not, but you are satisfied with your phone's battery life in standby, then no biggie. For the rest of the cases - condolences, but you can still install a third-party app that mimics the Doze behavior to a decent extent.