If you leave the 3g switch in your iphone settings on, will 3g still be used?

I just got a data package today and I was wondering, when you go to Settings> General> Cellular, and leave the Enable 3G/Cellular Data buttons on while your phone sits idle, will your data still be used and run out faster? I only have 2GB so I need to know before making a mistake and running out too quickly…

Yes, most apps on the market like facebook or stock apps like email (if you set refresh interval shorter) and etc gather bits of data to check for notifications. But this is pretty small amount, so its not a big concern. I say turn it off at night and then turn it on in the day. But the data used is small enough to not be a concern (only if a bunch of people are messaging you and you get bunch of notifications and stuff like that).