See, this is good for carriers that send regular updates and that have all these available features. For myself, although I'm with a carrier that is reputable and has good coverage (Fido in Canada), their support services suck. On my account it shows I've registered for Overage notifications yet, I don't receive any - it's similar with friends/family who are with Fido. It sends it randomly every few months saying "Dear XXXXX, You have used 400 out of your allotted 500MB limit (80%). To avoid charges please ensure you use only the given data or you will be charged X per 500MB". Another problem is that it is kind of tedious, I have to keep logging into their website and keep wondering how much space I have left. They way I'm thinking is it'll be kinda like the call block feature or whatever else is currently on iOS 7. If you don't need it - it doesn't interfere with your daily functions, but if you need it, it's there.
The problem is the inbuilt monitor is also a hassle. You have to manually know when you're billing date is and then reset it...which kind of sucks. Secondly, you're assuming that everyone has privileges similar to yourself. Kid you not, some carriers are terrible with things like this. If you look at carriers like WIND or Bell Canada, don't even get me started on how terrible they are.