Once users enable this mode, it will block background data usage; it sends a signal to apps to use less data in the foreground wherever possible. (indabaa.com)
A quick note before we continue: as we talk about restricting background data usage, we want to make it very clear that these restrictions only apply to your mobile data usage; even if you heavily restrict an application it will still function normally when you are on Wi - Fi. (howtogeek.com)
The option to limit background data usage, which was confusingly absent from ICS - based Galaxy S3 firmware, is now available in the Jelly Bean update. (androidcentral.com)