Why do I need a pre-interview? Will they learn anything new about me?
The application form and interview for GE is quite a bit more extensive than what is required for APIS (name, passport number, DOB, etc.) You are asked to list your past travels, past residences, information about relatives, etc. Further, your fingerprints will be taken and (I believe) they are run through some database
before your application is approved. (This is, I think, different from the ordinary entry process where your fingerprints are taken when you enter, but nothing is done with them in real time to approve or not approve your entry.)