I like to deactivate my 4G Data or Wifi when I'm not using it.
But whenever I activate Data (4G or Wifi), all the Cores of the CPU are being used at 100% and the phone becomes unusable for at least 30sec.
So it seems that All the APPS wants to go online at the same time, rather than one by one.
It's very annoying when I just want to go online for the GPS or the Browser : I have to wait 30sec minimum every time.
[Phone : Samsung S3 I9300 with Cyanogenmod]