I can help you here a bit here. I've been using and learning JD Ultimate for a while now,
With the screen options, this helps save tiny bits of battery usage. Basically you can go to your lock screen from screen off without turning on data until you actually unlock the phone.
Configuring apps is just that. You can set connection permissions for apps that use data/Internet. You can make the usual white list of apps that you need to have access to, and you can set the levels separately for apps you dont need hogging data, if they do.
You have to have enable selected under status to let the commands in Juice Defender become active aka saving bits here and there. If you swipe left to the About screen, you can see an average percentage of life saved over a period of time.
I am not sure what Juice Defender non Plus/Ultimate(Free) version shows on the status page because I have had the Ultimate version with all settings available for quite a long time. You can visit the online manuals thru the app. Not a bad read, but experimenting once you've got the basics down is best. I do believe it helps a bit, as I can go quite a while on low usage, wi-fi always on, screen going on and off. Under heavy usage, it just doesn't matter.