What this feature does is restrict apps running in the background from using up your mobile data while at the same time letting the app in current use enjoy full data usage. (nashvillechatterclass.com)
To prevent an app from running in the background in this way, you don't need to use the multitasking view. (howtogeek.com)
On Android, you can leave the game running in the background while checking your spreadsheet. (bgr.com)