Greenify's mane function is to hibernate any installed apps. This allows users to to quell overly active apps that are draining their battery without having to delete them. This can be done with or without ROOT.
Greenifying without ROOT has to be done manually each time
When using Greenify without ROOT access to hibernate apps, it has to be done manually each time. There is a widget and shortcut that users can set to their home screen to make this action a bit easier though.