It's both. And at the same time it isn't.
For instance, my MetaWatch requires an app to run in the background. Turning off BAR for that app changes nothing. But tracking apps only seem to half-work with BAR disabled.
But the real news about BAR is that the phone learns when you use for instance Facebook and updates the content shortly before you open the app so you don't have to wait for those few seconds it takes to update. A smoother experience
On the other hand, it seems like people who have news paper subscriptions and in iOS 6 had the content download automatically even when the app was killed (not in the multitask thingy), now have to actually go into the app despite having BAR activated and the app closed (not killed)...