Letting apps run in the background means that they can stay up to date – with news headlines or weather reports, for instance – and provide you with useful notifications.
How do you control it?
Most apps are set to run in the background by default. So, if you don’t want them all secretly sapping bandwidth and consuming battery power in the background, go to Start > Settings > Privacy > Background apps and scroll through the app list.
Switch off any apps you don’t need and leave only the most useful ones – Calendar, Maps, People, Photos, Settings and Store, for example – switched on in the background.