For questions related to background tasks (things running in background / when screen is turned off)
Windows Phone places more restrictions on background tasks than many other mobile operating systems.
Windows Phone 7 : The ability to restrict background apps dates backs to WP7 days.
Windows Phone 8.1 : In WP8.1 this setting was merged with Battery saver.
Windows 10 v1511 : Windows 10 Mobile enhanced this option further. it allowed the user to enable/disable the background activity of an app completely. In addition the battery saver settings allowed the user to choose which apps can run in background.
Windows 10 v1611 : bought an another option "Managed by Windows" to the battery saver settings. It is more smart as the OS will the background activity of apps that drain battery.