When I enable Restrict Background Data the pop up says that some apps and services will not work unless the device is connected to WiFi.
How can I know which specific apps and services?
The apps that requires constant internet connection and cannot be run without it. But they will notify you.
I've tried lots of apps but the only one of them complained about background data: Google play store. It doesn't want to work without background data.
All apps I ever used work fine with BG data restricted.
I recommend not use the restriction for downloaders, SoundCloud (if you are listening to the music, it will stop buffering after you minimize the app or turn off the screen); some messengers and email clients may stop receiving messages while phone is sleeping.