I am using greenify app for about 2 years.
It actually reduces the ram consumption of the mobile.
Onlike other apps it will not run all along in background and reduce battery but it hybernate the backrouund running applications according to the need of the user.
By doing this way we can also reduce the battery consumption by different apps.
One more thing to be noted is that it works more perfectly in rooted phones.
But because the app is hybernated, it will not show any nitifications of that particular app until we open it manually.but its actually very helpfull for me .