This tweak is perfectly match for users who don't use unlimited data plan. With it you are able to lively monitor your existing data usage condition in the status bar.
To enable this tweak to give you a report on the already used data usage or instead disabling this tweak can be done in the Settings area. And not just that, tweak also brings you an ability to set a data limit, which will track whether the usage has reached the limit you've set, if it reaches the limit Data Usage Monitor will stop you from using data above that limit.
Basically Data Usage Monitor offers the same service like WeeTrackData tweak and they are not free apps too, you need to spend about $2, to get the Data Usage Manager or WeeTrack Data.