The core of this program, as well as many analogues, is to deactivate unnecessary processes and expand device operations autonomously. Greenify makes programs run in the background to sleep – so they don't consume energy, but if you need an application and start consciously, it will work fully.
It must be realized that such decisions have clear consequences: push notifications stop running, messenger, alarm clock, etc. stop working, so think twice before making a sleep application.
Although there are some difficulties in understanding program functions, Greenify looks smart and simple, thanks to a simple and modern design.