Well I wonder what do you do that makes you to produce your CNIC thrice a day!
Anyways, some also use that for safety purposes as not to lose the original one, but they are not valid in case of any legal issue, like you cant have a challan on this CNIC, can not open up a bank account etc etc...
These can be used at casual checkpoints, as guest identifications at various buildings, and things like that.